A user posted this on another forum I go to and I thought it was pretty cool. It's easy to use and has multiple brushes to give the effect of sketches and such. I've yet to make anything worth posting, though. (I usually just goof around with it.) It's free and works in your browser. Just screenshoot what you made and post it here. The save button gives an image too big for the forums. (If you're drawing something small.)
Give it a shot.