PhotoFlare - Quick, simple but powerful Cross Platform image editor.
Krita - Krita is a professional FREE and open source painting program. It is made by artists that want to seaffordable art tools for everyone. Concept art. texture and matte painters, illustrations and comics.
PixBuilder - Free Photo Editing Software for PC
TwistedBrush Pro Studio - A powerful and unique natural media painting program.
PhotoDemon - Lightweight portable BSD licensed photo editor for Windows focused on performance and usability.
Corel Painter - Corel Painter is media painting software.