A new book worth considering (especially for those who have been before and have a good idea of what's there already, and are looking for that 'something different' factor) is
The Hidden Magic of WDW. It's not a comprehensive guidebook of the parks but it IS a look at a lot of the small-scale detail, Imagineer secrets and back-stories which many people miss, all written in narrative style with a loving affection for the real artistry behind Walt's creation.
And I should know because my wife wrote it