others
"As far as we can tell, your best bet for going small will rely on wares from Plat'Home and Buffalo Technology."
search for "single board computer", there are quite a few others - for example:
http://www.soekris.com/
http://www.bwi.com/index
http://www.pcengines.ch/wrap.htm
http://www.mikrotik.com/
most are geared towards router/access point type applications, but most also have options for storage (CF cards, 2.5" drives, etc.)