another one, didn't see if it was alerady added.

http://www.terabit.nildram.co.uk/tattoo/index.htm

Tattoo lets you paint directly on a 3D mesh in .3ds, .obj and a couple other formats.

mesh needs to be UV mapped beforehand ( either in the modeler or a 3rd party app like Lithium Unwrap)

has a veraiety of basic painting tools including airbrush, blend, smear, dodge, burn. adjust pixel size, opacity and step

biggest thing i noticed so far messing with it is you need as solid ( one piece) UV mapping as possible.

example if painting a head, you want as much of the head UV mapped all in one piece, other iwse you gt noticible gaps in the skin where UVs are seperated.

You do get to watch the 2D UV skin as your painting on the mesh so you can see the changed directly.



here i got a poorly UV mapped mesh and just spraying some colors on it just to try it out. need a far better UV mapping job done prior to tring to paint it.

there is a tutorial here on using Tattoo as well as this guy wrote several for Wings3D Blender and GIMP
http://www.pagodaproductions.com/tiki/tiki-page.php?pageName=Tutorials