I have two favorites when it comes to books for Disney trip planning. The first is The Unofficial Guide to Walt Disney World by Bob Sehlinger with Len Testa.
This book has more details than any book I've read. This is actually one you could purchase then refer back to a couple years later. But don't let it get too outdated or you'll miss all that's new in the parks. The book is updated every year and the updates are highlighted. If you're a first-time Disney visitor or haven't been there in many years, this is a book you'll want to buy.
My other favorite book is the Passporter Walt Disney World. Now this is a book that I buy for every year that we go. This spiral bound hard cover has a wealth of information about planning. This book was named one of Disney Magazine's editors' favorite source for planning a trip to Walt Disney World. This book is made to take along with you. In the back of your Passporter are pockets where you can keep receipts or airline tickets. It also has 10 days worth of pages so you can journal about your trip and log information like weather, the best thing about the day, the funniest and the worst. This is a great feature for anyone who travels to Disney because you can write down little details you want to remember for your next trip. It's also a good way to remember what the weather was during that time of year. In one section, the rides and attractions are described and rated by authors Jennifer and Dave Marx. Their daughter rates the rides also. Passporters tend to sell out quickly at book stores and are harder to find the further into the year you get, so if you know you're going, purchase one early!