Well, vampires and liches are always a favorite of mine.
In my world myth I had a PrC that watched/warded/walked the paths of the dead. One requirement was the cleric had to die, to take up their life in the demi-plane (the hallways of death/afterlife). The party could contact the cleric at temples and such. The cleric would also guide souls back to bodies as needed but mostly would lead the dead to the proper afterlife and try and stop some undead from leaving to go back to the prime plane.
I could see an interesting book on the subject.

In my world myth I had a PrC that watched/warded/walked the paths of the dead. One requirement was the cleric had to die, to take up their life in the demi-plane (the hallways of death/afterlife). The party could contact the cleric at temples and such. The cleric would also guide souls back to bodies as needed but mostly would lead the dead to the proper afterlife and try and stop some undead from leaving to go back to the prime plane.
I could see an interesting book on the subject.