Have you ever sketched with the online drawing tool, Scribbler Too? http://www.zefrank.com/scribbler/scribblertoo/
Fair warning, it can be quite mesmerizing! Above is one I did today. I like to go to Scribbler just to play around sometimes.
Below are some older ones. The last one was a popular selling tee shirt on my Red Bubble site, until I uploaded more paintings and drawings done in traditional media. Then they overtook it. But I still sell one of those once in awhile!