There's a new fanfic community called ironfic. Their intent is to end up being multi-fandom, but for now, they're starting out with BtVS and HP. Basically, it's a take-off on the Iron Chef program, using fic. A community writer and a challenger are each given a "special ingredient" and have a month to produce at least a 1000-word fic. There's judging, but really, it's not about that. It's about having more fic to read. :D Plus, being challenged to write new things.
There will be a het and a slash challenge every month, and they're currently looking for community writers. Some characters are taken (I'm going to be doing Spike), but there's still *plenty* left. Take a look; it sounds like it's going to be fun. :)