Gameduino - a game adapter for microcontrollers

Gameduino connects your Arduino to a VGA monitor and speakers, so anyone who can write an Arduino sketch can create video games. It's packed full of 8-bit game goodness: hundreds of sprites, smooth scrolling, multi-channel stereo sound.

Take one of the dozen sample programs, and be making your own game in minutes. You'll have fantastic retro graphics and sound with Gameduino's simple design, under the direct control of the Arduino. Perfect for the dedicated games writer, the weekend hacker, and the classroom.

Gameduino has thorough documentation and:

You can see more about it on the Gameduino project page.