Dave Caolo showed you an open source image editing tool, so I thought I'd pick up another end of the spectrum with an illustration tool by the name of WouldjaDraw. While it isn't open source, WouldjaDraw does have a healthy array of illustrating features and tools. Inspector palettes, gradient tools, a nice selection of export formats and a strong toolset should make WouldjaDraw a satisfying alternative to the illustration mega-suites.
A demo is available, and a license will run you a mere $29.95.
[via Daring Fireball]