Me and just about everyone else at school plays N. It can be downloaded or played in the browser for portability.
You can download it here:
http://www.harveycartel.org/metanet/n.html
Basically it's a ninja physics platformer with awsome levels, extra features, and competition. There is a main series of 100 episodes consisting of 5 levels. After every 10 episodes in a series, you unlock a new ninja "flavor" or color.
I've completed up to the lavender flavor.
How far have you guys gotten?