I recently bought a decTOP small form factor (SFF) computer. My goal was to build a cheap, fanless, quiet, and low power consumption Linux server.
It's at Librenix
This is a tiny computer, about the size of a Mac Mini. But, because it has no fan, it runs a bit quieter and, with the help of a 1-watt, 366 MHz CPU, consumes only 8 watts. For comparison, the G4 Mac Mini consumes about 20-30 watts, depending on load.