Dumbo.
The scene when he goes to see his mother in jail and the song Baby Mine is played, breaks my heart and reduces me to a blubbering wreck every time, I'm even welling up whilst typing this. I also love the Jazz singing crows.
I also love (in no particular order)
Sleeping Beauty
Snow White
Jungle Book
Cinderella
Fantasia
Lilo & Stitch
Mary Poppins (not strictly a cartoon I know, but you've gotta love those penguins!)
Bambi
Pinocchio
Hunchback of Notre Dame
Beauty and the Beast
Mulan
All the Pixar movies