In the fall, I think starting mid-Sept., they have Mickey's Not-So-Scary Halloween Party. They deck the place out w/ Halloween decorations, have a special parade, a special version of Wishes (Hallowishes, I think it's called), and in the evening everyone can come dressed up and collect candy at different booths. It's supposed to be lot of fun, though I've heard some parents say it really is too spooky for some young kids.
They of course also do a big celebration for Christmas. I'm not sure when that starts.
That's all I can think of right now. When is the last time you went, may I ask? Disney is always adding something new, and more likely than not there are a few new attractions you haven't seen yet that would help make the vacation more new and fun...for example, Soarin', Lights Motor Action, Cinderellabration, and Expedition Everest were all added within this past year or so.