Imagination Cubed - This is a collaborative drawing program. You can invite and friend and both draw from your own computers!
TuxPaint - free software! You can't beat the price! This is a great drawing program.

45 Websites for Students to Create Their Own Original Artwork

This is Dyane Smoke's blog. She describes each tool and gives them star ratings. Since she has worked so hard on her blog post, I'll not repeat it here, just send you to her blog!

For another extensive list of painting sites and comics, go to our Technology Keys wiki.