Hard to narrow down, but here are three of our favorites(we like to laugh:):
Madagascar(any age). My kids can't get enough of the crazy lemurs! And they love to dance to "I like to Move It, Move It!"
Despicable Me(any age). Those little yellow dudes are hilarious!
And for more of a "real" movie: A Little Princess(Any age also, but I think for a child to really follow it, 6 and up. Might not entertain younger ones). I think its a BEAUTIFUL story. I have three daughters and I think it teaches a wonderful lesson: All girls are princesses. All special. All important.