The Raspberry Pi is a computer about the size of a business card, with 2x USB2 out, an SD card for storage, Ethernet, HDMI out, analog video out, and 3.5mm sound out.
Here is a video of it running Quake 3 with 1080p output, 4x anti-aliasing and maxed graphics.
The price is going to be $25 without ethernet, and $35 with, when it is released in November. For more info, visit their website.