I am a first time planner, and have purchased numerous books and guides for the trip. I also spend about two hours a day combing the sites for information and guidance.
I. This board is the best source of information available.
II. Birnbaum's is the most colorful, and it is an easy read containing great information. Remember it is the "official" guide and therefore is approved by Disney for its content.
III. The Unofficial Guide contains the most information in a portable source. For first timers it is an invaluable resource. Some veterans buy it every year; however, I think your money might be better spent elsewhere.
IV. Passporter is the text that will go with me to The World. It is practical, compact and functional. A nice text that doubles as a journal and record holder.
V. Birnbaum's Disney for Kids by Kids is going to be under our tree this Christmas for our 5 1/2 yo. It contains great pictures and autograph pages in the back for character sightings.
VI. Walt Disney World with Kids is different than the title above and is the least necessary of them all, but a good book nonetheless if it is the only one you buy. I used it a lot at the beginning (it was the first book I purchased) but the others are clearly superior.
I have found that planning has become not a chore, but an obsession. So much to learn, and every book and website offers one common bit of advice: PLAN, PLAN, and PLAN.
Good Luck. You can get by without buying anything and just use the websites, or you can get crazy like I did, and spend almost as much on books as I will at Cinderella's Table for Breakfast on New Year's Day!
Peace,