Here are two slash fics. They are Btvs/SGA.
A Cosmo Boy's Guide to Dating by Allyndra [PG-13]
Summary: Despite being accompanied to the Pegasus Galaxy by a
ridiculously hot one-eyed man, Rodney had been home for nearly two
weeks without getting laid. Rodney/Xander Harris. Sequel to: Chances
Are. BtVS/Stargate: Atlantis crossover
Chances Are by Allyndra [PG-13]
Summary: Rodney wakes up to an unexpected morning after. Crossover with
You can find them here: http://www.wraithbait.com/viewuser.php?uid=1591
Enjoy, I know I did.