I've been playing with the idea of a Touhou contest, all songs (official and fan arrangments). I'd need to gauge interest first though.
EDIT: I'm also thinking about how to keep a contest from going on too long. Perhaps a set up where it's 2 matches a day + a match for the next round at the same time. Day 1 would be the first two matches of round one, Day 2 would be the third and fourth matches of round one AND the first match of round 2, and so on. Wouldn't start round 3 like that though.