Freeware Puzzle Games

What are the best physics based pc puzzle games like world of goo, crazy machines 2, etc etc?

im open to both commerical and freeware. im a big freeware fan, but will buy a great game.

Public Comments

1. You should really try this game called magic pen. It's a lot of fun and is a great physics based game. Great fun and free! Here's the link:
2. Portal, seriously, it's the best puzzle game ever. It's a pity it's short. Oh well, Quality > Quantity