For my money, there are only three books worth reading on the subject of necromancy and undeath in RPGs, and they are the Complete Book of Necromancers, Hollowfaust: City of Necromancers, and Van Richten's Guide to the Lich. Most other books are full of rather obvious variations on the same old archetypes, but these three just seem to ... breathe new life into the walking dead, so to speak. I heartily recommend them. Everything else is just footnotes and afterthoughts.
"I shall laugh as they place my head upon the block, laugh at them all as the raven jeers at the gallows or the worm mocks the grave. It took the Prince's most powerful knights to bring me -shackled in cold iron- before my earthly liege, but not before I had slain a hundred of his retainers, twisted the insides of his lovely wife, cursed their only son with ravening madness eternal." - Nebt Bhakau, The Book of Shadows
"You cannot practice the Art when you are happy, nor advance in its study if you are content." - Kazerabet, The Art of Necromancy