The Genius MousePen 8x6 is a pressure-sensitive graphics tablet that lets you draw freehand in programs like Corel Painter. Usually such tablets start at around $80, and large ones like this run even higher, but Amazon has it for just $39.99 with free shipping.
I'm no tablet expert, but the reviews on Amazon and this one on About.com peg this as a pretty solid model (the ratings average 4 out of 5 stars). It features 1,024 pressure-sensitivity levels, a wireless pen, a wireless mouse, and a copy of the aforementioned Corel Painter. Although the specs indicate Windows compatibility only, the Genius site has Mac OS X drivers available for download. If you're in the market for a tablet, this is the deal to beat.