The Complete Book of Necromancers

I simply loved the stuff in this book. It's a wealth of lore, additional rules, and flavor for necromancy. Take note that this book is not meant for player characters but mainly for DMs to craft villains and necromancy-related campaigns. Of course, there's nothing stopping you from allowing them.

The book delves into character creation and performs a simple analysis of necromancers. There are 7 necromancer kits introduced in this book plus five new non-weapon proficiencies. The book also has two chapters dealing with necromancer role-playing. Other stuff includes lots of wizard and cleric spells, interesting magic items, information on necromantic minions and religions. The book ends with a detailed mini-campaign.