Crayon Physics is a bit like the iPhone app Trace, so it looks like a lot of fun. It won the Independent Games Award in 2008, whatever that is.
We've put it on our wish list in the Bowl. It is a 2D physics puzzle / sandbox game, in which you get to experience what it would be like if your drawings would be magically transformed into real physical objects. Solve puzzles with your artistic vision and creative use of physics. Check out their website for more details.