The fit-PC looks like a very interesting platform for ET projects. It is cheap ($285), small (4.7x4.6x1.6 inches), low power (3 to 5 watts) and very capable:

• 500 MHz AMD Geode LX800 processor
• 256 MB of DDR RAM
• 40 GB hard drive
• Dual 100 Mbps Ethernet
• SXGA graphics controller, resolution to 1920 x 1440
• 2 USB 2.0 high speed ports
• Audio in/out interfaces
• RS-232 serial port
• Single 5V power supply