Here is a development board sold by Atmel for their AVR7000 series MCUs. It runs Linux and is available for $69.95 from several sources, including AVNET.
The ATNGW100 Network Gateway Kit could make a nice little (and inexpensive) Linux based robot controller. 
Yes, I have my eye on one of these… 
This is the kind of controller that could make on board audio/video processing for a robot a reality. The AVR7000 series MCUs are designed for multimedia processing.
8-Dale