http://benblogged.com/ It's free! Well, I felt guilty, so I paid him an honorarium. Of course, I'm prejudiced— he posted an invitation I designed that used some of his art.
Ben draws his work by hand in Illustrator (can we really still use the terms "draw" and "by hand" to refer to something created digitally?). I have also been playing with Live Trace in Illustrator and, with much tinkering, have gotten some interesting results.