Perfect Balance is an excellent and simple web-based physics puzzle game. Get all of the tetrids to balance to move on to the next stage. I spent the evening addicted to this yesterday and made it through the forty “Harmony” stages. The “Inferno” stages are less interesting because they all unlock simultaneously, so there is no measure of your progress.
I think what is so compelling about the game is that there are multiple solutions to many of the puzzles. If you balance in some ridiculous, yet successful way you advance just the same as if you had balanced the way the designer intended. If you have a spare hour (who doesn’t in this economy?), check it out.