This is a short instructional video from Dave Hax showing how to draw near perfect circles with no extra tools. Basically you just keep your hand stationary and pivot the paper around your hand. You can use different pivot points on your hand to draw different sized circles. It's as simple as that. Me? I've drawn so many cartoon titties in my day I can draw a perfect circle without any tricks AND WITH MY EYES CLOSED. *closes eyes, drawing* Well? "That's a penis." That's just how good I am, I've moved past circles.
Keep going for the video.
Thanks to Justin, who traces the bottoms of empty orange juice concentrate cans like a normal kindergartener.