LinuxDevices.com has a report on the latest ultra small single board computers that are out. Some are smaller than credit cards, several fit in DIMM sockets, and all of them are more powerful and have more memory than my desktop PC had just a couple of years ago. These boards are based on a variety of CPUs including the Intel x86, StrongArm, ETRAX, and Motorola PowerPC. If you're looking for a new SBC for your next robot, there are a lot of good ideas here.