What about a script which accepts pictures emailed from camera phones, and a web frontend that displays them on the site? Then allow people to comment on the pictures etc?
Think how handy it would be to be able to quickly snap a picture of something on your phone when you're out, and post it to the site instantly.. i wrote something like this for my personal site (php/mysql) and would be happy to donate the code..
obviously people would need to register first, and there may have to be some sanity checking or a grace period involved. but it's a unique idea and I don't think anyone else is really doing it..