I am using a soekris net5501. It pulls about 0.5A at 12V for the machine and a small disk, and runs i386 code. I have a 2T USB drive plugged in externally, and am using 2 of the 4 ethernets. The only real downsides are that it's expensive and mass storage options are somewhat limited (and 100 Mb/s, not 1Gb/s), but it's a nice board in a nice metal case.
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