Maybe I'm just a sucker for 8-bit-style games, but I'm really enjoying Gamma Bros. It's a space shooter that comes in web-based Flash as well as downloadable Windows and Mac flavors, and feature pixely graphics and fast action. You play as one of the Gamma Bros. who must destroy an endless stream of UFOs that invade from every direction. Use the arrow keys to move your craft around and the WASD keys to fire in four cardinal directions. When your energy gets depleted, running into your brother will swap your ships, tag-team-style. The rest is easy to pick up, but a solid challenge to complete.