One of my very favorite apps for the Mac is Autodesk's Sketchbook Pro. I use it all the time for sketching because it's digital pencils feel just about as close to the real thing as you can get. I use the pencils so much I've kind of neglected the other great tools the program has. Last night I tried to rectify that by playing with the digital markers and brushes. The result is this sketch of Princess Leia.