I know Exemplars of Evil is, but I just found out Elder Evils contains one of my fave baddies ever- Zargon from B4 If so, I may pick it up on the cheap.
P.S. You'd think WOTC would have chosen to title these books differently to avoid confusion
Zargon's in there, along with some other creative foes. Highly recommended.
I play/run Savage Worlds and a little 4e, and this is the only 3.5 book I went back and bought, and one of only two 3.5 books I'm keeping (Lords of Madness is the other).