Among the Small Form Factor (Desktop) PCs I looked at, I also found some Linux boxes.

The Shuttle XPC series of barebones systems come with no Operating System pre-installed, as far as I could see. They are ideal for installing Linux (according to the gurus at ixbtlabs)

A smaller option that is quite unique is the CherryPal Desktop – it is about the size of a Nintendo DS, and its Operating System in based on Debian/GNU Linux. There is a review of it here at Gizmodo.com. CNET’s Crave also has a small article about the CherryPal Desktop.

A Nettop would also classify as a Small Form Factor Desktop PC, so I could not leave out the Asus Nettop. The Asus Eee Box Desktop is also a green SFF, using only 20 watts of power. The original Asus Eee Box came preinstalled with Windows XP Home, but the newer ASUS Eee Box B202 has Linux pre-installed.

Other Linux SFFs are the fit PC and the linutop. Linutop is also available as a bootable 1GB USB key!