Ben Nye make a great paint and they come in various sizes. Look at a nearest, Costume/Haloween, or Theatrical store. I've only used this brand but it works very well in a air brush or other types of equipment.
I've used everything from theatrical grease paint (tough to clean off though-use baby oil as the first step) to tempra paints which come off with soap and water. Also with the tempra paints you can get some really neat effects as they dry and crack giving lots of texture.
All the body painting that I have done with Leroy Roper has been using theatrical makeup. You could contact leroy roper at firstname.lastname@example.org or go to his website www.leroyroper.com. When I have been painted this stuff washes off easily