Every year [link|http://www.idevgames.com|iDevGames] has a game programming contest. The winners as well as the other entries can be downloaded for free from [link|http://www.udevgames.com/downloads/?cid=3|uDevGames].
It's kind of a mixed bag, but I've found a couple that are pretty addictive so far:
- [link|http://www.udevgames.com/downloads/?dlid=23|Ark-Annoyed] - A clever re-imagining of my old Amiga favorite, Arkanoid.
- [link|http://www.udevgames.com/downloads/?dlid=16|Snowball] - A cute little 3D maze game.