An overview of small Linux systems

Some boards don't need any blobs or non-free drivers: Bubble, (and its predecessor Balloonboard3) are ones I know about in detail, carefully designed to be Free and Open and have parts you can still get in 5 years time, precisely to avoid the 'throw-away hardware' problem. http://iendian.com/

Anything with a GPU on needs a non-free driver, but you may or may not need the GPU part, and free drivers are slowly being produced (I'd currently pick hardware with a Mali in as the first one likely to get a useful free driver).

There are an _awful lot_ of boards/devices missing from that list. Not sure exactly what the listing criteria are, but off the top of my head: Efika Smarttop smartbook, Toshiba AC100, Samsung Origen, DN320, Excito B3, MV2120, Dockstar, GoFlex, Netgear Stora, QNAP TS-11x -21x -41x, Raidsonic IB62x0, SS-4000E, Openblocks AX3 A6, Hercules Cafe, Technologic systems boards, plus loads more older hardware.