I thought this would be useful for modders. The Foundry is now offering MARI free for non-commercial use. This is a top-of-the-line texture painting tool (the commercial version costs $2000 to give you an idea).

I can't personally speak for the software. While I use The Foundry's modeling tool, MODO, my texture work is done in Substance Painter 2. (Which is a whole lot cheaper for commercial use and uses procedural materials, which rock).