Most of my paints are actually Americana. Its water based you can get it at Micheals, Hobby Lobby, etc. Real cheap about a dollar or so, but some of the colours (yellow, red, and a couple of the really really dark colours) don't cover very well and it takes a couple of coats but, other than that they work great. And it pretty easy to match with GW stuff, not exactly the same but they are really close.
The_Outcast