My two cents:
The WOTC D&D books are of surprisingly variable quality. Although I had planned to purchase the new DDG, I was disappointed to discover that it is the only book that actually got worse with 3E, something I scarcely imagined possible considering how terrible it already was. The Epic Level Handbook, I also returned to its shelf when I read the epic level Paladin abilities -- I actually laughed out loud in the store.
Manual of the Planes, on the other hand, I had absolutely no intention of buying. I had planar travel and never use it in my campaigns. However the alternate cosmologies section I actually consider to be the finest thing WOTC has produced for D&D, with the possible exception of the Players' Handbook.