So I thought it'd be easier to find good stories pairing characters across fandoms. Turns out? A lot of fics excel in concept and fail utterly in execution. Not these babies, though! These are awesome. Some of them are obviously destined to exist (Vala/Captain Jack) while others come out of the clear blue (Narcissa/Wesley), but they're all on this list because their authors made me Buy It, if only for the duration of the story.
Warning: These stories contain character death, crossgen, crossovers, het, infidelity, one night stands, noncon, slash, time travel, and UST.
01.
35 Minutes (Seth Cohen/Julian Sark) [The OC/Alias]
02.
Close Your Eyes and Think of England (Veronica Mars/James Bond) [Veronica Mars/James Bond]
03.
The Things I Cannot Change (Simon Tam/Lex Luthor) [Firefly/Smallville]
04.
Xi Ji Ba Yuan (Simon Tam/Julian Bashir) [Star Trek: Deep Space Nine/Firefly]
05.
prince of thieves (Patrick Stump/Remy LeBeau) [RPS/X-Men]
06.
Friday Night Drinking Games (Rogue/Jake Foley) [Jake 2.0/X-Men]
07.
she can drive as fast as me but she stops at all the lights (Captain Jack Harkness/Vala Mal Doran) [Torchwood/Stargate SG-1]
08.
The Honey Trap (Captain Jack Harkness/Duncan Macleod) [Torchwood/Highlander]
09.
Getting Drinks (Dean Winchester/Hannibal King) [Blade: Trinity/Supernatural]
10.
Now You're Messing with a Son of a Bitch (Dawn Summers/Dean Winchester) [BtVS/Supernatural]
11.
In the Key of Major Finn (Lorelai Gilmore/Riley Finn) [Gilmore Girls/BtVS]
12.
Practical Linguistics (Xander Harris/Jack O'Neill) (WiP) [BtVS/Stargate SG-1]
13.
Deja Vu (Xander Harris/Harry Potter) [BtVS/Harry Potter]
14.
Older and Far Away (Xander Harris/Remus Lupin) [Harry Potter/BtVS]
15.
Quid Pro Quo (Wesley Wyndham-Pryce/Narcissa Malfoy) [Angel/Harry Potter]