I purchased a SheevaPlug[1] a couple years ago. It's a plug sized ARM server consuming 5W max. It's been great for a low-power, always-on debian server. For the lazy or not capable user, there is the Pogo Plug[2], which was prototyped using the Sheeva. You plug in ethernet and a usb hard drive, and it gives you access from the PogoPlug site.

[1]: http://www.globalscaletechnologies.com/p-22-sheevaplug-dev-k... [2]: https://pogoplug.com/devices