Elizabeth, great call on Tekkonkinkreeto (which for you non-Japanese speakers is a play on 'tekkin konkreeto' which is the pronunciation for "steel-reinforced concrete" in Japanese). I think the movie is masterly.
I agree with above posters that the Incredibles, Triplets of Belleville, and Cars have great audio and animation. I am surprised that noone has mentioned Fantasia, which to me is the original animation set to music movie.