I just stumbled upon a Geode NX 1750 and replaced my underclocked Barton 2500+ with it, and it works great. It's actually faster than my previous system, because I had it clocked at 100 mhz x 11 = 1.1 Ghz (~40w) and the Geode is 133 mhz x 10.5 = 1.4 Ghz (14w).

I had to underclock the Barton (via FSB) to reduce 12v power consumption for my M2-ATX.

I had hoped to underclock the Geode to 1.0 Ghz (100 mhz fsb) and go fanless, but the system ran too warm. Oh well.