A friend of mine recently turned me on to a cool freeware game called Knytt Stories.  This is a very cool and well designed 2D game that I spent a few hours on last night.  The graphics are not fascinating and the control is relatively easy, but the design and power ups you get to complete each adventure is addictive.  Plus the developers included some very cool relaxing music playing in the background. 

This is cool game to carry around on your flash drive as levels are easily saved.  Also included is a neat level editor to create your own worlds.  Or you can also download additional levels from the Knytt site.

Download Knytt Stories