Found some cool mini PCs on E-Bay (not my auction, just thought people might be interested):
Designed as set top boxes, they have an onboard Cyrix 233mhz CPU, has TV out, VGA, LAN, sound plus an ISA/PCI slot in a very small case. Seems to be based on a SBC, so it probably only requires +5V and +12V to operate (includes 45W AC PSU).
The 233 CPU probably would not handle DivX or even DVD very well, but for someone looking to do MP3 and GPS this could be a good solution. I'd get one myself but I'm in Canada and seller wont ship outside US
Here's a link to the manufacters website: