Along with the ones Branch recommended, I would also suggest more Yami no Matsuei prompts, and some prompts for Saiyuki, Tokyo Babylon-X/1999, Wild Adapter, Weiss Kreuz, Gundam Wing, GetBackers, Count Cain/Godchild, and Angel Sanctuary, which are all fairly popular fandoms.
On the RPF front, maybe at least one each for k-pop and j-pop? I can name some specific artists if that's easier. Like Branch, I'd love to participate and pimp out OTW, so I'm naming things that would draw the part of my flist who mostly aren't into live-action fandoms. The part that is into live-action fandoms already knows about OTW. *G*