My son is 3 1/2.
Cars (love the first one!)
Mater's Tall Tales - he's been asking for that a lot recently.
Ice Age - there are 3 movies, he's watched them all but really only likes the 1st one.
Rio - we recently watched that and he asked to see it again (we did it through redbox though and didn't have it anymore) so that's going on our Christmas list :)
The Little Engine That Could - found that on Netflix - I enjoyed it.
He really likes Thomas, Word World and Curious George too. I DVR'd the 3 Curious George movies and we've watched the Christmas one a bunch of times. He likes the 2nd one with the train/journey for the elephant too.
I did put on Beauty and the Beast for him and he sat through it once, but he only did that cause it's one of my favorite movies (and he has told me many times since it's my favorite movie, not his, so he won't watch it. haha!)
Tinkerbell movies - I DVR'd them from the Disney channel and he likes watching those. His favorite is the recent "Pixie Hallow Games" which is only 30 minutes.
WALL-E is another one he asks for.
The Fox and the Hound - he watched that one with my husband and liked it, but hasn't shown much interest in it since.
He really likes watching Mickey Mouse on the Disney channel too, they have a few hour long episodes/movies that he will watch. (He has decided Minnie is his favorite (for now) and really likes watching the Minnie Bowtique shorts they've had on.
There are a few other great suggestions others have mentioned (Land Before Time, Winnie the Pooh,...oh and don't forget An American Tale!) but he hasn't shown any interest in watching those.
My in-laws said he watched The Jungle Book with them and enjoyed that.