A few weeks ago we reviewed nootropoic design's Hackvision arduino-compatible game console. The Hackvision is a great standalone device, but if you're looking to get your retro game groove on and want to use your existing arduino, Wayne and Layne's Video Game Shield for Arduino is the way to go.
The Video Game Shield has everything you need to play and make your own video games, including graphics, text, sound effects, music, and built-in support for to two Nintendo Wii Nunchuck or Classic controllers.
If you're still wondering if you can live without one, check out Tetris on the Video Game Shield:
Now available on InMojo: Video Game Shield for Arduino by Wayne and Layne
"Wayne and Layne, LLC makes open source hardware. Their kits come with easy-to-follow illustrated instructions and explanations of how the kit works. All the schematics, PCB artwork, and source code are provided under open licenses."
InMojo supports the Open Source Hardware Definition v1.0