Ten One Design showed off their Inklet trackpad tablet software for the Mac. Inklet is a $25 application that allows you to use your MacBook, Pro and Air multi-touch trackpad as a pressure sensitive drawing tablet. The drawing area is shown in the second screen and can be resized (pinch/zoom) and panned around (two finger drag). This video shows it in action:
Macworld hosted a DEMO presentation showing off 6 of the "best of" products being shown at the expo.