For the last few months, retailers have been clearing out the Diamond Mako, which is the US version of the Psion Revo Plus. Its a fine device with a 36MHz ARM 7 CPU, 16MB of RAM/storage, IR port, and a 480x160 monochrome screen. Its fairly well supported on Windows, but not so well on Macintosh or Linux. It has a built-in keyboard, which actually works OK, and is a nice clamshell design. Connectivity to the outside world is via IR or via the docking cradle to 9-pin serial. There are free tools for doing C++ programming for the device from Symbian, but due to the lack of external storage and proprietary chipset, there is little progress in making a Linux port.

I got mine for $109 from ubid.com, but the price there depends on the current demand for the device. sparco.com has them for $134. It seems near impossible to find a true Psion device anymore, since they stopped making them around July 2001.