I'm searching for resources on undeads in general and their creation, as I want to develop a new realm for my homebrew setting, in which necromancy and magical-alchemical research on undeads, diseases, death, decay, ghosts... is the main cultural aspect. Those necromancers would create undead monsters by magical devices, alchemical potions, dark rituals, simply stitching several corpses together or conjuring demons to animate the corpses (which would be in different states of decay). (As an example, take a look at the Scourge / Undead faction of World of Warcraft)
Right now I found some references on "Open Grave: Secrets of the Undead" by the WotC. But I'm not limited on D&D, I only need the fluff, not really the rules.
My question then is: Do you know any other material on this topic? Which books can you recommend?