Malagor's dead (assuming I'm thinking of the right person), I don't know a whole lot about Eldrad except he's from Ulthwe and I don't know who any of the rest of those are. But if we're going to talk about Avatars (only one kind of which I know actually exists) we might as well include the actual chaos gods
@Starsign: Someone correct me if I'm wrong: Apothecaries only treat other space marines (they're specialists, they only can treat space marines. Like how a doctor can treat a human but not... oh, say a puppy. They could guess, but since they don't know precisely how the other's body works...), and that particular device is the Emperor's Peace - euthanasia applies to the temple for a marine who's going to die but is doing it slowly.