The fandoms are listed alphabetically.
Space Kitten, by Basingstoke. Het and slash (though there's no romantic focus, so it feels quite gen), Richie/Amanda, Duncan/Methos. (ca. 2,900 words)
These are more glimpses at a universe than a fully realized story, but the setup is just very cool.
1967 Plymouth GTX Convertible, Black., by Basingstoke. Slash, Dean/Gunn, Angel, Sam. (ca. 2,100 words)
This one is just a lot of fun. They first meet over anti-zombie supplies, there's banter, Sam and Angel are playing euchre... also Dean/Gunn! (also on AO3)
Days Like This, by Killa. Gen, Angel, Dean Winchester. (ca. 9,200 words)
Dean and Angel meet on a hunt, and fight a gross, tentacled monster, but really the best thing in this story is the banter and the many great lines. (also on AO3)
Downloaded series, by Ennyousai. Slash and het, Kirk/McCoy, Scotty/Six. WIP (for the series, the stories are finished)
I'm not familiar with BSG, but the author's notes said it would work if you just knew ST and it did work great as a Star Trek AU.
Lost Horizons, by Shadadukal. Slash, Charles/Erik, Nikola/Erik, Nikola/Harry Colebourn. (ca. 8,350 words)
An X-Men crossover with Sanctuary and A Bear Named Winnie, how could I not like it? In some places the story gave more of a summary when I wished it to show all this stuff in detail, but I liked the setup. (needs AO3 account)
Abnormal Psychology (on AO3) (ca. 1,440 words) and A Sam Adams Moment (on AO3) (ca. 1,500 words), by Siriaeve. Gen, Sweets, John Sheppard.
Sweets working for the SGC is just an awesome and funny premise.
Stray Cat Blues, by Mary. Gen, Faith, Sam, Dean, and John Winchester. (ca. 3,500 words)
This takes place pre-series for Supernatural. The Winchesters run into Faith while on the road. (Sadly, I don't have a working link to the story anymore.)
Better Know an Alien, by Salieri. Gen. (ca. 1,200 words)
This was simply hilarious.
In Darkness, by Mhalachai. Gen, Aaron Hotchner. (ca. 3,700 words)
The premise here is that Hotch is squib who left the magical world, but his son has magic. I really enjoyed the squib perspective here.
The Time Has Come to Be Gone, by Jujuberry136. Gen. (ca. 28,950 words)
I enjoy stories with the Criminal Minds team meeting and dealing with the Winchesters, and this one is a good action/case story. (also on AO3)
When You Are Done, by Jujuberry136. Gen. (ca. 27,140 words)
This is the sequel to The Time Has Come to Be Gone, that I recced in the past, and just as much fun. I liked the casefile, and that there was some comic relief mixed with the horror. (also on AO3)
Defect (ca. 39,600 words) and its sequel Hell, and Back (ca. 42,000 words), by Kikkimax. Gen, ensemble.
This is set after the second season finale of Supernatural. While Sam tries to get Dean out of the deal with the demon with the help of Bobby and Ellen, Dean is taken into custody by the FBI and interrogated and evaluated by the BAU team. I really enjoyed the take of the profiler team on Dean, and how they try to make sense of him and revise their opinions without ever actually buying into Dean's supernatural worldview. (unfortunately I only have Wayback Machine links to these)
Eat it Twilight, by liliaeth. Gen. (ca. 45,775 words)
Crossing these universes is a match I really enjoy, and this one gives a great outsider POV on the Winchesters, and the story worked well from both series' worldbuilding perspectives.
To Conquer Fear, by Mara G. Gen, Gil Grissom, Batman and their teams. (ca. 2,800 words)
They work together to catch the Scarecrow in Las Vegas. The story is told mostly in emails and more on the fun than on the angst side of things. (also on AO3)
Office Hours (on AO3) (ca. 10,000 words) and the sequel The Wisdom to Know the Difference (on AO3) (ca. 30,000 words), by Tartanshell. Gen, Peter Parker, Hank McCoy, Matt Murdock, and Scott Summers.
Peter meets Hank (at first not yet blue) as one of his biochemistry professors in college. This is just an awesome and very entertaining crossover, that has a great blend of humor and angst.
Agents of Fortune, by Karasu Yurei. Gen, Dean Winchester, Sam Winchester, Alec, Lydecker, Renfro. WIP
So far this seems to be a basic "let's make these characters meet" crossover, but it has a plot that makes sense and the way the universes are mixed is interesting. It's not exactly the canon universe for Dark Angel in that there was no Pulse, but it still feels more like a crossover than an AU premise. X5-494 is given the mission to kidnap Sam for the Manticore program, so he tries to impersonate Dean.
With a Bang, by Mink. Gen, Alec, Dean Winchester, Sam Winchester. (ca. 42,000 words)
This is a good action-adventure, and I liked how the shows' mythologies were meshed, even though I'm not that into the whole breeding cult arc of DA season two. Also Alec, Sam and Dean together are just fun to watch.
Begotten and Gingerbread, by Nilchance. Gen, Alec, Sam Winchester, Dean Winchester, Boby Singer. WIP
I'm not actually sure whether this is a series or a WIP, but I find it intriguing so far, because in this crossover the timelines of DA and SPN don't seem to have been messed with to mesh them, but instead Alec somehow ended up in 2008, though neither he nor the Winchesters seem to know the how or why yet.
Hailing From Parts Unknown, by Sister Wolf. Slash, Logan (Wolverine)/Alec (X5-494). (ca. 3,500 words)
Alec and Logan and cage fights. Why wouldn't you read this?
Travelled on his looks, by Petronelle. Gen, Fraser, Ray K., Dick Grayson, Tim Drake. (ca. 2,200 words)
I'm not much interested in crossdressing, but Fraser and Ray teaming up with the Batclan here was fun.
Five Superheroes Dean Winchester Never Slept With, by Derry. Slash and het, Dean Winchester/Roy Harper, Dean Winchester/Stephanie Brown, Dean Winchester/Grace Choi, Dean Winchester/Dick Grayson, Dean Winchester/Jason Todd. (ca. 3,250 words)
The title really says it all. Dean just fits so very well into the DCU. The idea behind the Dean/Steph snippet is especially cool, but Dick and Dean bonding over their scars and Dean working with Roy were also great. (also on AO3)
The Once And Future Pain In My Ass, by Ras Elased. Slash, Merlin/Arthur. (ca. 6,000 words)
Normally I'm not that interested in fanfic that transposes Merlin to present day and has him look for Arthur's reincarnation, but mixed with Dresden Files like in this story it works for me, because Merlin hires Dresden and we get his POV on the Merlin scenario. Unfortunately this story doesn't give us their whole quest, but even this setup of their first meeting is a lot of fun. (also on AO3)
For I Have Been a Stranger in a Foreign Land, by Mortigi_tempo. Slash, Kirk/Spock. WIP (ca. 10,000 words so far)
This is a very cool crossover setup. Kirk and Spock get stranded on Arrakis.
Birds of a Feather, by julia_here. Gen, Benton Fraser, Rodney McKay. (ca. 15,500 words)
It's set mostly pre-series for both DS and SGA, but also has a section set after the SGA finale, so there are spoilers for that. I liked how the author made these two universes fit well together. Besides Rodney and Fraser bonding over how awful Alberta was for them, and their different ways of not fitting with the Beaver scouts, I especially loved the hints of bizarreness in what happened when they met again, that felt very much like the typical DS events.
Chicago, by Carol. Gen, Carol Hathaway, Dean, Sam, John. (ca. 4,900 words)
I like outsider viewpoints, so looking at the pre-series Winchesters from Carol Hathaway's POV was really neat.
The Noodle Fic, or Mama Bears Don't Stand Aside, by Tassos. Het, John/Aeryn. (ca. 13,290 words)
I've followed this as a WIP, and now it is finished and quite awesome. Don't mind the odd title, this is a solid crossover, in which John and Aeryn scrape by post-PKW, and end up working with Mal and his crew because they need a doctor for D'argo. (also on AO3)
Flying Low at Night, by Cofax. Het, John Sheppard/Aeryn Sun. (ca. 8,600 words)
It's set in the same universe as Cofax's story Bellum Interruptum but I hadn't read that and still understood this story. Sheppard and Aeryn just go together like hazelnuts and chocolate as far as I'm concerned. Sheppard here is stranded in the UT, and provides a great outsider POV of Aeryn and the others. (also on AO3)
Tomorrow and tomorrow and tomorrow, by Tassos. Gen. It's a WIP, but the parts stand well on their own. (three parts with ca. 36,700 words, the fourth is unifished and abandoned)
Crichton ends up in the Pegasus galaxy, is culled, but becomes a Runner, and finally meets the Lanteans. The first part is entirely from Crichton's POV and the story has a great way to integrate Harvey and generally show us the wackiness that's the inside of his head. Once Crichton comes to Atlantis it's just as awesome. It has great interaction between Crichton and the Lanteans. (also on AO3<7a>
Crooked Paths, by themonkeycabal. Gen, Rodney McKay, John Crichton, Aeryn Sun, Moya. (ca. 8,100 words)
Rodney ends up in the UTs, comes across Crichton, who is an old college rival of his, and grudgingly asks him for help to get back to Atlantis. This one is fun to read, I laughed a lot.
Untaken Roads, by Tassos. Gen, Dean Winchester, John Crichton. (ca. 4,500 words)
This gives us another glimpse at Crichton as Runner, like in the previous FS/SGA crossover by Tassos that I've also recced. And seeing him interact with Dean is just fun. (also on AO3)
Unwilling Oracle, by Beatrice Otter. Gen, John Crichton, Kira Nerys. (ca. 1,870 words)
This has a really cool premise meshing the wormhole mythologies.
An Unlikely Meeting, by Cofax. Gen, Sam Winchester, Dean Winchester, Chiana, Rygel, John Crichton. (ca. 1,030 words)
This just a snippet, more an opening into a universe than a full story, but what we get is such a cool crossover setup that it's worth pointing out regardless. (also oon AO3)
The Monster in the Closet and the sequel A Heart That Beats in Time With Yours, by Shaye. Het, Rodney/Kaylee. (ca. 3,200 words and 2,200 words)
Rodney and Kaylee meet as prisoners of the Reavers, so it is rather dark.
Eight Crazy Pilots Serenity Didn't Keep, by Tassos. Gen. (ca. 2,600 words)
These snippets about the Serenity crew encountering different pilots are just cool. My favorite were the ones with Luke Skywalker and John Crichton. (also on AO3)
Riggins & Winchester, by Bone. Slash, Tim Riggins/Dean Winchester, also Billy Riggins, Sam Winchester. (ca. 4,800 words)
The Winchesters are passing through Dillon. This gives a great look at the characters, also of course it's hot.
Shotgun, by July. Gen. (ca. 18,000 words)
This is also a bit of an AU, because of course in canon the Winchesters moved around a lot, but it feels more like a crossover than an AU. An the idea of Sam and Dean growing up in Dillon while John still hunts is simply awesome.
Necessary Changes, by DevilC. Slash, Jason Street/Scott Summers, also Logan/Jean and some other pairings, both het and slash are implied. (ca. 24,000 words)
Jason discovers he's a mutant on top of everything else and is invited to attend the Xavier Institute. I'm really liking Jason here so far, and also his friendship with Tim, and of course I always have a soft spot for stories with Scott. (also on AO3)
Clarke's Law, by Isis. Gen, ensemble, primarily Carson, Rodney, John, Hermione, Harry. (ca. 21,300 words)
The way the mythologies of HP and SGA are mixed and integrated here is just cool.
Different Kinds of Magic (also on AO3, by Rokeon, and its remix, by Zvi. Gen. (ca. 750 and 695 words)
Both of these are short, but still make the universes fit together great, with a cool take on John.
Old Country, by Astolat. Slash, Sam/Dean. (ca. 40,600 words)
I don't read a lot of Wincest, but I think this crossover is a great read even if you prefer gen. It's a lot of fun, humor mixed into the angst and drama, and the merge of the Potterverse with SPN here works great, and I liked the take on goblins and their magic in particular. (also on AO3)
Winchesters at Hogwarts series, by Ignipes. Gen. (so far three stories with ca. 10,400 words)
In this crossover AU John dies and Sam and Dean are sent to wizard relatives in England, so Dean attends Hogwarts. (also on AO3)
Curiosities (on AO3, needs account) (ca. 4,045 words) and Stutter (ca. 1,500 words), by Penknife. Slash, Erik Lehnsherr/Charles Xavier, Tom Riddle, Lily Potter, Sirius Black.
Recently Penknife offered to write timestamp fic, and I noticed that I never recced the original crossover for which I requested a timestamp. Anyway, in the first Erik Lehnsherr encounters Tom Riddle in 1950, the timestamp is set during the first Voldemort war/the Marauders era, and both are interesting and well worth reading. (unfortunately the sequel has been locked, and is not on AO3)
Knight's Gambit, by Killa. Slash, Methos/Alva Keel, Duncan/Methos implied. (ca. 4,000 words)
I admit that I was a little bit lost with the demon plot in this story, because I know very little about Highlander (I've only watched a handful of the first season ages ago and a couple of xovers), but I couldn't resist the allure of Miracles fic. Even missing some of the Highlander context, this was still a very cool x-over premise, not least because Alva as an immortal would not just fit with him knowing all those languages, but explain why that investigation firm of his apparently doesn't really needs to earn money, yet he can still pay his employees. (also on AO3)
Untitled snippet, by Pentapus. Gen. (ca. 230 words)
This is just a brief snippet, but it is a very neat idea to merge the mythologies of the two shows.
To Become Immortal, First You Have to Die, by ShadowLoverK. Gen. (ca. 3,200 words)
Kirk is an immortal and has his first death from an allergic reaction during the movie.
Charm City by Hth. Slash, Sam/Tim. (ca. 7,630 words)
I've only watched Homicide sporadically, but the relationships here between Sam and Dean as well as Tim and Sam really pulled me in.
Slash-Evidence series by Saundra. Slash, Fox Mulder/Tim Bayliss.
This crossover series is a classic: Great casefiles, mixed with a developing relationship. Unfortunately some of the later parts are only found online in newsgroups archives anymore, though others are at Gossamer. To make finding the individual parts easier for you I collected the links in an LJ entry, and am linking to that one here, rather than to put links to dozens of parts here directly.
New Jersey Voodoo, by Rokeon. Gen. (ca. 1,020 words)
This is short, but really funny. John has a relapse back towards Bug!John, starting with an at first innocuous rash and progressing from there, and House tries to diagnose. (also on AO3)
My Brother's Keeper, by Ducks-in-a-row. Gen. (ca. 9,400 words)
Sam is in a coma for supernatural reasons, and Dean clashes with House and his team, all in a way that is a lot of fun to read. I think these mesh quite well because it's not like House's procedures and patient interactions are anything like happens in hospitals, so throwing in zombies does not stretch the House universe of wacky medicine too far.
Rebuild the Bridges in Your Mind, by st_aurafina. Gen, Greg House, Robert Chase, with implied Chase/Cameron and Chase/Jason Stryker. (ca. 25,600 words)
In this Chase is mutant. It's a really solid crossover that makes House mesh well with the X-Men universe.
Actualize This, by Helena Handbasket. Gen. (ca. 35,600 words)
Usually I dislike the "characters of different series meet at a seminar" crossover device, but this one is really funny, and well worth reading. (also on AO3)
What Keeps The Light, by Eisoj5. Gen, Dan Vasser, Sarah Connor. (ca. 3,000 words)
I'm a bit ambivalent about this one, because I would have liked to learn so much more of what happened. In a way it is more the start of what could have been an longer story. OTOH a timetravel crossover mixing Journeyman and Dan's involuntary timetravel with the Sarah Connor Chronicles is such a great fit, and I really like the setup here and the possibilities their meeting here opens. (needs an AO3 account)
Bad Pennies, by Troyswann. Gen. (ca. 4,000 words)
This crossover seems like it could be right out of a MacGyver episode, only better because the SG-1 team is involved.
Verity, by Kathryn Andersen. Gen. (ca. 35,900 words)
I had some problems with the story, for example I think that Jim and Blair have a prophesied destiny in this version of the Matrix universe is overkill (one prophesied messianic figure is more than enough IMO), and wouldn't have really been necessary for the story, and I would have liked a slightly more prominent role for the Matrix characters, but overall I quite enjoyed it.
Lovers and Dreamers, by Alexia Eve. (9,472 words)
This Smallville/Muppet Show x-over, is not only hilarious, it also truly works. Lionel together with Waldorf and Statler, what more could you want?
Take Atlantis, by Siegeofangels. Gen. (ca. 800 words)
This is quite short, and doesn't really have a plot beyond "the Muppets visit Atlantis", OTOH having the Muppets on Atlantis is awesome and funny. (also on AO3)
What Kind of Day Has It Been?, by Victoria P. Gen, Dean Winchester, Sam Winchester, Kermit and the Muppet Show ensemble. (ca. 3,300 words)
I love Muppet crossovers (felt rules! *g*), and this one made me laugh a lot.
A Story Just Begun, by bergann. Slash, Colby Granger/Evan Lorne. (ca. 3,930 words)
This is an "SGC goes public" story, set after season 5 and assumes that they can't hide a floating city in the San Fransisco Bay. I liked how that was handled and thought Numb3rs was fit in well. (also on AO3)
Redefinition, by bluflamingo. Slash, Colby Granger/Evan Lorne, Cadman/Simpson. (ca. 6,790 words)
This is more angsty than happy, but I liked this take on how hard it must be to have a cross-galaxy relationship. (also on AO3)
Crooked Line, by miss_zedem. Slash, Charlie Eppes/John Sheppard, Charlie/Colby. (ca. 8,600 words)
This is set during The Return for SGA, but its premise is that there was a relationship between John and Charlie in the past and they are meeting again for a temporary reunion. I really liked that this was low on the relationship angst and drama, yet not a PWP either. (Sadly, I don't have a working link to the story anymore.)
Connecting Dots & Straight Lines, by This Fish Flies. Slash, John Sheppard/Rodney McKay. (series, ca. 2,500 words so far)
This is mostly fluff with the premise that Sheppard is somehow related to the Eppes, but fun to read.
Down The Rabbit Hole, by Bluflamingo. Slash, Colby/Lorne, Colby/Daniel. (ca. 10,000 words)
I like how this handles the relationships, the complications that come with dating outside of your secret alien conspiracy, and the way the SGC happens to tangle with the FBI here works for me too.
Unexplained (ca. 4,260 words) and its sequels Explained (ca. 4,340 words) and Doubt (ca. 8,300 words), by ALEO. Gen, Don Eppes.
During a serial killer investigation Don runs into the Winchesters. I enjoyed Don's outside POV of Sam and Dean here. In the last one the Supernatural world functions more as a vehicle for Don-whump than as equal crossover partner, but it's not as if I dislike seeing Don hurt, and angst while he adjusts his worldview to the supernatural.
Take a Long Line, by Derry667. Gen, Dean Winchester, Sam Winchester, Don Eppes, Charlie Eppes, Alan Eppes. (ca. 22,000 words)
The Winchesters are trying to stop a psychic arsonist at CalSci, which we see through the eyes of the Eppes. I liked how competent Sam and Dean were in this story as well as the the outsider look at them. (also on AO3)
The People You Meet, by Mandy's Bitch. Slash, Chris Keller/Rodney McKay. (ca. 8,300 words)
I rarely read crossovers when I just know one of the sources, but I followed a rec somewhere, and the story pulled me in. I have never actually watched any episode of Oz (so I can't judge Keller's characterization), but I think it is pre-series for Oz as well as for SGA. Anyway, it starts when Rodney gets robbed by Keller, and things get more complicated from there at a fast pace.
Leapin Lizards, by Gwendolyn Grace. Gen, Sam Winchester, Dean Winchester, Sam Beckett, Al Calavicci. (ca. 18,560 words)
Sam Beckett leaps into John Winchester when Dean and Sam were still children. There is a good case story, and Beckett has to deal with finding out that the supernatural is real, and handle two young Winchesters. (also on AO3)
Untitled, by Siriaeve. Gen, Aiden Ford, Ronon Dex, Rodney McKay, John Sheppard, and the Endless. (ca. 750 words)
It's a "Five Things" type story in which SGA and SG-1 characters meet the Endless, and while each vignette is short, they are also gorgeous. (Sadly, I don't have a working link to the story anymore.)
Seven Moments, by Barrowjane. Gen. (ca. 1,300 words)
There's just something about other characters meeting the Endless that I really enjoy, and this example of the genre is no exception.
Harvester of Eyes, by gwendolyngrace. Gen. (ca. 26,000 words)
John Winchester hunts the Corinthian, meanwhile Sam and Dean get lost in the Dreaming. This crossover is a great blend of the two sources.
The Mutant Problem, by Katt. Gen. (ca. 7,900 words)
This is a very cool multimedia fanfic in the form of a fictional photo essay by Peter Parker.
Don't Mention the Wookies by Cate. Slash, McKay/Sheppard. (ca 1,400 words)
I waffled a bit whether this really counts as a real crossover, but I found its slightly wacky premise cute and funny, and it is definitely crossover-ish, so I included it in this rec set anyway. (also on AO3)
The Old World, by aesc. Slash, John Sheppard/Rodney McKay, Dean Winchester, Sam Winchester, Castiel. (ca. 10,890 words)
They all run across each other on Earth while hunting wraith. This mixed the mythologies of the two shows in a cool way. (As a side note, even though the author labelled it McKay/Sheppard slash, it read gen to me.)
All Worlds Converge To Where You Are by Gottalovev. Slash, John Sheppard/Dean Winchester, John Sheppard/Rodney McKay, Dean/Castiel. (ca. 45,800 words)
This has the brilliant premise to mix the SGA alternative reality Vegas-verse with the SPN potential dystopian future from 5x04 The End. The two meshed very well, and I really liked seeing the Supernatural world through Sheppard's POV.
And All the World Beneath, by Jenn. Slash, John Sheppard/Dean Winchester, John Sheppard/Rodney McKay. (ca. 67,000 words)
This is a very cool and creepy apocafic, meshing Stargate and Supernatural in a way that makes sense for both mythologies.
Untitled SGA/SPN snippets, by kitsune_tsuki WIP
So far more an enticing glimpse at a backstory and an opening snippet than a single story, but I thought the premise that Sheppard grew up as a hunter like Sam and Dean, and now encounters creepy supernatural stuff in Pegasus was cool.
Rollin', by tzi and zaganthi. Slash, Rodney McKay/Dean Winchester. (8,256 words)
This isn't a pairing or crossover that would have occurred to me, but strangely it works.
Only Someone Running, by busaikko. Slash, Rodney McKay/Brendan Dean. (ca. 7,800 words)
This crossover has awesome plot twists, and meshes the two universes well. It is rather sad though.
Voyage par Mer, by Sealie. Gen, John, Rodney, Carson, Grant. (ca. 30,000 words)
This one is a good take on the "Rodney and Grant are related" premise. There are more parts available in her LJ here. (also on AO3)
White Rabbit, by Valderys. Gen, John Sheppard, Grant Jansky (the author labelled it as being "pre-slash if you squint" for a bunch of pairings, but I read it as gen). (8,866 words)
This was done for the reel_sga challenge and adapts the movie Harvey. After an Ancient technology mishap John finds himself back on earth and in the past, and only Grant Jansky can see him. Donald's, Jack's and Adam's reactions to Grant seeing an invisible Air Force Colonel are great, it is a lot of fun to read. (also on AO3)
Floodlights on the Highway, by Thassalia. Gen, Dean, Cam, Vala. (ca. 3,770 words)
How could you not enjoy Cam and Vala meeting Dean at a car show?
People Who Repair Quantums, or Five Planets The Enterprise Never Visited, by Ignipes. Gen. (ca. 2,800 words)
Star Trek: Reboot/Alien/Discworld/Doctor Who/Dune/Star Wars
I really enjoyed the crossovers for which I was familiar with the sources, also, while I don't know Discworld, the bit where Spock reacts to the flat disc and giant turtle and so on in space was awesome. (also on AO3)
a fucking space opera (or Six Characters Who Didn't Board the USS Enterprise), by Oxoniensis. Gen. (3,169 words)
Star Trek: Reboot/Harry Potter/Merlin/Stargate Atlantis/Supernatural/Terminator: The Sarah Connor Chronicles
In the best tradition of wacky crossovers, this was simply a lot of fun.
Nor Hell A Fury, by Lucy Gillam. Gen, Sam Winchester, Dean Winchester, Dennis Guilder, Christine. (ca. 14,800 words)
I haven't read Christine, but this was still a very enjoyable casefile type of story with neat twists in the the car's background. So if you like to read about the Winchesters hunting monsters or evil cars in this case, you should give this a try. (also on AO3)
On the Use of Weapons, by Cofax. Gen, Ellen Harvelle. (ca. 1,600 words)
In this snippet Ellen observes Sarah, John and Cameron at a gun show, and it gives a great outsider POV of the three. (also on AO3)
Angels in the Architecture , by Davincis_girl. (ca. 12,000 words)
I think the two universes are a great mix, especially when it comes to the various teenage experiences of growing up with pseudo-military training, and here John Connor travels back to 1999 and gets the teenaged Sam and Dean to help him. (also on AO3, though for some reason the last chapter isn't posted there)
Once Upon a Time in the West, by Marina Rusalka. Het, John Winchester/Sarah Connor. (ca. 7,660 words)
John and Sarah meet while buying weapons and ammunition. This makes for an awesome and very fitting pairing (not to mention hot), also Sam and Dean have some hilarious lines. As usual with Marina Rusalka's SPN fic the view we get of the Winchesters' pre-series family life is great, even if this is John-centric and not focused on the brothers.
Brothers in Arms, by SylvanWitch. Gen, Dean Winchester, Derek Reese. (ca. 2,440 words)
Dean runs into Derek while hunting, and somehow these two shows just go together like chocolate and hazelnuts.
Woman Inflammable, by Vehemently. Gen, John Winchester, Sarah Connor. (ca. 4,660 words)
I really enjoyed this insight into John at the beginning of his hunting life, and the outsider look at Sarah. And of course John would have the worst luck in that that he picks Sarah Connor & Co to run into early on. (also on AO3)
where the grass is green and the girls are pretty (ca. 2,165 words) and its sequel oh, won't you please take me home (ca. 2,700 words), by Vorrothiel. Gen, Ash, John Connor.
There's something about crossovers between Supernatural and Terminator that really appeals to me. The universes just go together like hazelnuts and chocolate, IMO. Anyway, this one has the unique premise that Ash used to know John Connor in high school. (Sadly, I don't have a working link to the story anymore.)
Pass the Pork-Barrel Salt, by Gwendolyn Grace and Etakyma. Gen, Sam Winchester, Dean Winchester, Josh Lyman, Donna Moss, C.J. Cregg. (ca. 5,000 words)
Josh meets the Winchesters during a "Big Block of Cheese Day". This crossover is simply a lot of fun.
Stopping for Pancakes(on AO3) and its sequel Looking for Salt (on AO3), by dotfic. Gen, Sam Winchester, Dean Winchester, Dana Scully, Fox Mulder. (ca. 950 and 5,800 words)
If you're interested at all in Supernatural you probably have already read those two. Anyway, it's great to have Mulder and Scully interact with the Winchesters. The first takes place pre-series when Sam and Dean are still kids and Mulder and Scully are still working for the FBI, and in the second they run across each other again years later, some time during the first SPN season, and are fighting zombies together. I mean, zombies, how could you resist that? *g*
Nothing Like Billy, by Embroiderama. Het, Ellen Harvelle/Fox Mulder. (ca. 2,622 words)
There isn't much plot beyond the sex in this crossover, but there was enough characterization and a plausible reason for their meeting to not have the story feel arbitrary.
Bright White Light, by lilacsigil. Gen. (ca. 35,000 words)
This is set during the X-Files episode "Fallen Angel", which I barely remembered, but the story still worked for me. We get the events of the episode but seen from the perspective (and worldview) of young Sam and Dean. I thought it was really cool how one side believes it's all aliens, and the other it's all supernatural and I was wondering what was really going on. And I liked Sam and Dean adventuring. (also on AO3)
Late Nite at the Sudzy Dudz, by Sarah Ellen. Gen. (ca. 3,500 words)
I have no idea how I could have missed reading this story for so long. This crossover is a lot of fun. I guess you could sum it up as "Mulder and Scully meet the Wincesters in a laundromat and talk about cattle mutilations." but the dialog is awesome and it made me laugh a lot, while still being plausible and in character within both series.
Northern Lights, by Sarah Ellen. Gen. (ca. 9,700 words)
In this one we get an outsider POV of the Winchester family as Mulder and Scully run into them during an investigation.
Bent, by Rachel Martin. Gen, Dean Winchester, Sam Winchester, Ororo Munroe, Scott Summers, Logan. (ca. 12,300 words so far) WIP
This is set during the SPN episode Benders. Scott thinks that one of the Winchestes is an out-of-control mutant and goes to search for them to stop the deaths he thinks the Winchesters are responsible for. (also on AO3)
Case X-1743: Unresolved, by Minisinoo. Het, Mulder/Scully, Jean/Scott. (ca. 24,500 words)
While still working on the X-Files Mulder and Scully investigate the incident at Scott's high school when his powers first manifested. Years later Mulder notices Scott during Jean's tv appearance and they meet again. The plot is mostly just about getting the characters together, but I really liked how the universes meshed here.