I'm basically just looking for something to play around, install new kernels and see what use cases for such a device I might find...
The DreamPlug looks interesting, as does the D2Plug.
I've had a Sheevaplug development kit running for over a year. I've replaced the power supply with an external one. It works well. But if I were wanting a new tiny computer now, I'd wait for this:http://www.raspberrypi.org/
"An ARM GNU/Linux box for $25."
Supposed to come out later this year.