These nifty little physics-based puzzle games have shown up on various lists at work:
Launchball lets you place tiles with different properties to get a ball to the goal. Some of the tiles provide power, some use power and some push the ball in different ways.
Crayon Physics is another ball-to-goal game but you draw shapes to apply force to the ball or guide it along its path.
The guy(s?) at Kloonigames are working on a Deluxe version of the Crayon Physics games that lets you use shapes and constructs other than boxes:
Both are a lot of fun and very addictive.