I downloaded the trial version of Sketchbook PRO and it's wonderful for sketching/drawing. The pencil tool has a nice feel to it. Though the interface of the program is a bit confusing, it's still fun to draw with.
Here are some sketches:
Black and white drawn in Sketchbook Pro:
Drawn in Sketchbook Pro, colored in Photoshop:
Drawn and colored in Sketchbook Pro: