Perhaps you could rent a movie instead? Only because I can't think of any fun movies you might want to see, other than maybe Ice Age like others have suggested. Harry Potter 6 was good, but not really party entertainment, unless everyone wants to discuss it afterward at a coffee shop.
The Proposal, while I'm not normally into fluff-type movies, I heard was actually very good and very funny. PG-13 though, depending on what age you are turning, heh. Or how about roller skating, or my personal favorite, ice skating! If you've got the rink. Disco night skating is fun.