I run a d20, Call of Cthulhu-style game with just one 'supernatural stuff' class. It's a spell-point based system with skill checks to cast spells. The spell list is pretty much just 'tell me what you want to do, and I'll tell you what level it would be'. It's designed for a low-magic setting with the Grim and Gritty hit point rules, so things are generally lower powered than they would be in a standard D&D setting - particularly damage-dealing magic and healing. At the moment, it's accomodating... a half-vampire, a werejaguar, a witch, a paladin, and a Buddhist monk. All have at least a level or two of Adept.
If you'd like to take a look at the (really skeletal) rules I've got for it, let me know, and I'll put them up on a web page somewhere.