On LiveJournal, there's a community called 30_lemons. The rules are simple; claim a pairing, sign up, and write thirty lemons (if you're not sure what the term means, it's the equivalent of a PWP) based on the thirty themes. For a complete list, go to http://community.livejournal.com/profile/30_lemons. You might find some other pairings you like as well. The ones I've written so far are listed below, complete with the theme I used.
Through a Glass, Darkly
(NC-17 - This place is . . . special.)
(NC-17 - Do you want to know how much I hate myself for this?)
(NC-17 - It's not just about the physical.)
Under the Influence
(NC-17 - What the hell did they give you?)
Capture the Flag
NC-17 - I caught you, I got you.
One on One
(NC-17 - Sweat, games, and basketball.)
(NC-17 - I thought we weren't going to talk about that.)
Wish I Might
(NC-17 - Starlight, Starbright . . .)
(NC-17 - Not for the first time, he wonders what he's doing here.)