From the back of the book:
Enter the Unholy Warrior, a towering figure of depravity and unspeakable evil. He wields fire and sword in the name of dark masters, spreading blood and terror in equal measure. The Unholy Warrior's Handbook gives you everything you need to introduce this core class to your campaign, including:
4 new prestige classes, including the Angel Hunter and the Knight of Bedlam
21 unholy warrior domains and their associated special abilities
25 new feats, including Blasphemer and Reckless Attack
A plethora of new spells and magic items
Dark masters and unholy orders: the gods and fiendish powers of evil and the unholy warriors that serve them
New and variant mounts, such as the Carrion Crow and the Mammoth of Baal
Rules for fallen paladins and redeemed unholy warriors
Deliciously evil art
The perfect compliment to the Book of the Righteous, Legions of Hell, and Armies of the Abyss, The Unholy Warrior's Handbook takes an unflinching look at evil's most dedicated servants.