Attached Link: http://www.cix.co.uk/~colbeck/graffiti.html

Well I'm not sure if this is in the same league as ZBrush, Painter, Deep Paint, Body Paint, etc. but believe it or not there's a free program that will allow you to paint directly on 3d models called "Graffiti". I haven't downloaded it myself but if any of you want to check it out, feel free.