The Imagineering books people have mentioned are great! I love looking through A Behind the Dreams Look at Making the Magic Real.. there's so much information and great art. I also really enjoy The Imagineering Way: Ideas to Ignite Your Creativity. It has tons of interesting anecdotes and inspirational messages and drawings, especially if you do anything creative.
Miss Bell mentioned this, but if you're really interested in Imagineering and the design of Disney World, there's an interesting book called What Would Walt Do? by a structural engineer who worked on building the Magic Kingdom. Though it's more of an autobiographical work, there are some interesting tidbits that I enjoyed, like how Walt wouldn't let them use cheaper girders for the construction of one of the rides, even though the engineers said they were adequate. He wanted everything to be top-of-the-line. There's also some interesting stuff about what Orlando was like before the parks were built.
Married to the Mouse sounds great. I'll have to pick that one up somewhere.. and John Hench's.