I've read a few books about WDW and Walt Disney, here are my recommendations.
1. Since The World Began by Jeff Kurtti - This is a great book with lots of pictures and art covering the first 25 years of WDW.
2. Remembering Walt by Amy and Howard Green - This book is a rememberance of Walt Disney as told in the words of his family and friends. Lots of great pictures and stories.
3. Disney War by James B Stewart - The is a very detailed account of the Eisner years of the Disney company. There's not too much coverage of WDW history, but it is very interesting to see how Eisner grew to company to what it is today. WARNING: This book doesn't really have much Disney Magic, it contains quite a few curse words and F-bombs, so beware.
4. Spinning Disneys World by Charles Ridgeway - This is a fantastic book with lots of great stories from both Disneyland and WDW. If you are a fan of The WDW Radio Show, then you know this book won't disappoint.
5. Walt Disney by Neal Gabler - This is a HUGE biography of Walt Disney, a very good read.
6. Of course you have to pick up both of Lou's trivia books, they have a ton of great trivia and info. And I know the year is 4 months old, but I also recommend his page a day trivia calender as well, fun park facts for each day.