Another vote for the UG. I soak up all the information I can get, so I love UG (and especially its occasionally snarky tone), the DIS, and subscription site Tour Guide Mike (a sponsor of the DIS boards). Be warned, though, the UG runs over 800 pages, no pictures (although it has illustrations), and isn't afraid to be critical of Disney. I just bought the 2008 edition, and I really like the following: the variety of touring plans w/ supplemental information on their site; the illustrations providing the layouts of Disney's resort rooms; and the details to the reviews.
I think the Passporter is useful, too, especially if you like the binder/folder design. It doesn't really work for me, as I prefer my to create my own organizational system, but lots of folks like it.