The Picture Show Man has a page dedicated to books on film coming out in 2008 and there are several covering aspects of animation. I don't know anything about these books except for what the links to Amazon have to offer. In no particular order:
The Idea of Nature in Disney Animation by David Whitley.
The Colored Cartoon: Black Representation in American Animated Short Films by Christopher P. Lehman.
Stepping into the Picture: Cartoon Designer Maurice Noble by Robert J. McKinnon.
Working with Walt: Interviews with Disney Artists by Don Peri.
The Mouse Machine: Disney and Technology by J.P. Telotte.
And the paperback version of The Animated Man: A Life of Walt Disney by Michael Barrier, the only book on this list I've read and one that I highly recommend.