Look at the BONE creeper. It comes in two versions last I looked. I have both. The difference is bigger wheels, color, and price. I like them both. They take a lot of abuse. The down side is that they take up a lot of room when you are trying to get under something. Also, check the bolts that hold the casters. So far, my favorite creeper is a piece of cardboard.
http://www.bonecreeper.com/
