Prestige class style books:
Masters of Arms - a neat system presenting dozens of "weapon" and "style" specialist type classes. All class abilities are also usable as feats, and the maneuvers are explicitly measured in power, and a system for making your own maneuvers is included.
Spells & Magic - one of my favorite magic books (BoEM I & III are also favorites, but less so for the classes.)
Quint Wizard, Monk, Rogue, and Sorcerer. Especially sorcerer. Neat stuff.
New Class Style books
Shaman's Handbook
ED: Shamans
Beyond Monks: Art of the Fight
Quintessential Chaos Mage
Mindscapes is a great classbook for psions, but if you want the 3.5 revamp, you'll have to wait for Hyperconscious.