At the risk of being so-unhip-it-hurts, here's my list:
Pinnochio - possibly one of the most artistically beautiful animations the Disney studio ever did.
Fantasia - It flopped at the box office, but has since been recognized as a film very much ahead of its time.
Dumbo - It's one of my favorite Disney musicals. It's fun to watch, and the songs stick to your brain like glue.
Sleeping Beauty - The production design for this film was by the controversial Eyvind Earle who, along with Mary Blair and the art-house rebels at United Productions of America (UPA), helped change the look and feel of animated cartoons for better and, debatably, for worse.
I'll post more as I think of them. For now, here's one of my favorite pieces of Disney character animation. Directed by Fred Moore. Production designed by Mary Blair.
https://www.youtube.com/watch?v=HzXIekb0WOI&feature=related