In reference to "what about Toy Story", technically that's Pixar not Disney (They started out as part of Lucasfilm, then Apple, then Disney as of 2006), plus it's not classic animation, but I agree it's awesome
I voted for Beauty and the Beast.
It was a tie between that and The Lion King for me, but I ultimately like Beauty and the Beast slightly more. My other major favorites are Sleeping Beauty, Little Mermaid, Mulan, and The Rescuers
The recent Princess and the Frog was pretty good as well, and I'm looking forward to the upcoming Rapunzel/Tangled too