In my mind the best books are as follows:
Hornsaw: Forest of Blood
Shelzar City of Sin (Especially if you want a more Arabian flavor)
Divine and the Defeated (Much better than Deities and Demi-gods, stats not withstanding)
Edge of Infinity (Not exactly ground breaking but I do love the Zodiac Planes)
The Player's Guides (Better than their 3.0 (and in Complete Divine's case better than that one), Splat book counterparts)
R&R 2
Creature Collection Revised, CC 2 and CC 3
Vigil Watch: Secrets of the Assatthi (sweet look at the S&SS' own snake men. In some ways I feel it's better than Serpent Kingdoms but I think that's because it only focuses on one race instead of like twenty.)
And yes Hollowfaust. (H-O-L-L-O-W faust folks.)