My own take:
Go to the library or bookstore. Plan on spending some time. Pick a Barnes and Noble with some comfy chairs. Read a few pages from each book and see what fits your style.
The big three around here:
Birnbaums - I like Birnbaums - especially for first time visitors. It has color photos, an upbeat attitude and it isn't overwhelming. However, its the simpliest of the books and being "official" everything is good. Which lets you make your decision on what sounds interesting to you, but you might want some more advice.
Passporter - Dave and Jen (the authors) are obviously Disney freaks. This book is great for planners and has pockets in it to keep your stuff and take notes about your trip. Its the most "workbook" like and as a veteran of the parks, its the book I buy for each trip - if only because it lets me put my tickets, etc. in pockets.
Unofficial Guide - Bob and Len and company have the best and most complete touring plans. IMHO, their attitude is a little commando, and the information overwhelming. I also don't find the data to be very accurate (making PSs online, or still having Le Cellier as a cafeteria years after its switch to a steak house). They also do an unfortuate job of stating opinions as fact - for instance their attitude of "every small child will need to go back to the resort for a nap" tells me they've never met my kids. This one is, however, far and away the most data packed book. However, the book is very well liked by a lot of DISers (if not by me, I still buy it occationally because I'm a queuing theory geek).
There are plenty of other books as well, and one of them may be even better for your needs than the three mentioned here.
Web sites:
Tour Guide Mike - a fee based "electronic book." Having used it, I think the paper books have more info, easier to access and I can carry them around. A lot of people print the TGM articles.
www.wdwinfo.com - home site to the DIS boards, contains a wealth of information for free. Still has the same problem of not being able to take it with you.
www.allearsnet.com - my favorite of the Disney information sites, Deb does a great job of letting people know what's new.