I've read numerous books about Disney but the main one I've read and keep coming back to is:
The ILLUSION OF LIFE: DISNEY ANIMATION by Frank Thomas and Ollie Johnston
If you're looking for the definitive "bible" on Disney animation, this is it. Written by two of Walt's "nine old men", it's a brilliant offering on the history and the technical aspects of Disney Animation from the early days on to today.
Tom (... amazed!)