Image Editors
GIMP
It is a freely distributed piece of software for such tasks as photo retouching, image composition and image authoring. It works on many operating systems, in many languages. Use it for editing web graphics, photos and more.
ArtRage
This program is designed with tablet users in mind. Be sure to get the free version.
Inkscape
Vector graphic editor. Inkscape's main goal is to create a powerful and convenient drawing tool fully compliant with XML, SVG, and CSS standards.
Xara Xtreme
It is primarily a vector graphics program, but is one of the new generation of cross-over products that handles photos and drawings with equal ease. They say it should work for the Macintosh as well.
Skencil
Vector drawing application. It should work on the Mac also, but you'll have to read up on how to do that.
