I just saw the 99 Euro / US$130 CuBox from Israeli start-up Solid-Run:
This is a small cube 2.17 x 2.17 x 1.65 inches (55 x 55 x 42mm), with connectors for power, two USB, eSATA
CuBox is essentially the same as Globalscale's US$249 D2Plug, but in a smaller package:
I think both are based on Marvell's SheevaPlug reference design.
I actually considered getting a D2Plug recently as a new workhorse computer, but I didn't have confidence that the software was really ready. I'd wonder the same thing about CuBox, since "open platform" too often means "you're on your own". JMO/YMMV