Seeing Mike put up a link to Sitronix, I was reminded of this interesting project from last year:

"Use a cheap digital photoframe as a second display for your PC"
http://spritesmods.com/?art=picframe&page=1

It turns out that some models of cheap ($20?) keychain jpeg viewers use a Sitronix 6502-like ST2205U, and that they have a backdoor in the firmware which allows some limited hacking.

Did anyone here look into that? Know any models of keychain available with the right hardware inside?