Comment Some phone handsets almost perfect for the task (Score 1) 273
Two that spring to mind are the Nokia N900 which already runs a format of *nix, Maemo. Probably pick one up on ebay pretty cheap. But slow and not much graphics ability, but has Web server ports of all sorts available via a nice easy apt-get.
Possibly more useful for many would be the Nokia N8, complete with hdmi out and apps like 'Big screen' and both dnla serving and client software etc. You can even hook up a wiimote with official Nokia and Noka beta labs software without any hacking or soldering.
The power consumption on these devices is tiny, there's definitely phone devices that will do a lot of what a pi can, on original firmware.