This site gather information helping repurposing some of the cheap picture frames on the market to use Linux, in any shape or form.
Parrot DF3120 This 320x240 frame can be bought for peanuts. It has 8MB of ram, a SD slot, and an ARM9 running at 266Mhz.
It currently can be tricked into running linux, to be used for example as a USB device "screen" for another board, like the bifferboard
O2 Joggler aka OpenPeak [links to external wiki site] Was available mostly on the UK market, but packs awesome hardware for (at the time) 50GBP. Atom core at 1.3Ghz, dual threads, 768M of SDRAM, capacitive touchscreen and so on... If you can find one, get one...