I've always held pencils in a strange, and eventually painful way, but that's what I'm used to. I let the bottom of the pencil rest against my ring finger, the above two resting next to each other on the top of the pencil (close to where the buttons are on a Wacom pen, but further apart) and the thumb just rests around the pencil so its tip touches the side of the index finger.
It's a weird position... I guess that position helped make my pencil drawings so damn small. It's perfect for the tiniest of movement. Hurts to write with for long periods of time...