Just a little while ago, I got a really interesting commission. I was given a few GW plastic kits and told to create some kind of Greater Daemon from all of it.
One of the advantages that the current Chaos Space Marine codex has over its predecessors, is that all of your daemons can be unique entities. So there isn't very much need to use only the daemons that Citadel Miniatures actually produce. I even know of a good deal of Nurgle forces have been converting Ghoul miniatures into their daemons, and some Khorne forces have been using beastmen.
Anyway, here is a Greater Daemon for the Black Legion. He was made from Minotaur and Chaos Spawn bits, along with a generous amount of Gray Stuff.