I've been having some great fun playing some games lately that all rely on physics. You really got to check some of these out as they allow some great use of imagination and rewards you for hard work and intelligent problem solving.
Armadillo Run - Try to get a ball from one place to another using anchor points and primatives (metal, rope, rubber, elastic, and even rockets!). You can try the demo version, but I'll tell you its VERY well worth the cost of the full version ($20) and the community is really growing with weekly contest and promised improvments from the game creator himself.
Bridge Builder - A simple GUI that allows you to build a bridge using metal rods across varying degree's of gaps. Fun and easy to learn.
Stair Dismount - Ever wanted to push someone down the stairs but in fear of hurting them? No worries now! You can push down a 3D model using various forces and angles to increase the amount of damage the fall down the stairs creates. A lot of fun and good laugh.
Make sure to check out
Fun-Motion. A website dedicated to physics based games, a great place to check out tons of interesting games.