Be Jackson Pollock (left-click to change colors)
Paint with a Brush or a Bucket
Paint with a Bigger Toolbox (requires a Shockwave plug-in download - it's safe!)
Explore the Elements and Principles of Art - the animations are fantastic!
You'll need to do a screen capture if you want to save your art.
(Thanks to lpapanicolaou at The Incredible Art Department forums for many of these links.)