I used Art of the Incredibles a lot when I was working on my short film, but I think my personal favorite "Art of" book would be the Art of Ratatouille - some of the character concept sketches are just amazing.
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The Art of Ratatouille
The Animator's Survival Kit: A Manual of Methods, Principles and Formulas for Classical, Computer, Games, Stop Motion and Internet Animators
The Animator's Survival Kit, Expanded Edition: A Manual of Methods, Principles and Formulas for Classical, Computer, Games, Stop Motion and Internet Animators