Birnbaum's is the Official Guide but it really only looks at the happy side of disney. I get it for the great pictures.
The Unofficial Guide has a lot of great information and tips. Passporter is good, although it doesn't have as much info as the Unofficial Guide, it has some handy dandy little pockets. You can take it with you and write in it every day so you have a journal of your trip and put tickets, etc. in the pockets.
WDW for Kids by Kids is great for (guess who?) kids!
Have a great time planning.