I've just received a FrogPad portable keyboard, to use with the OQO UMPC I bought recently. It's Bluetooth enabled. The manufacturers claim one can reach 40wpm quite quickly, even for those who aren't already touch typers. I'm most definitely a "hunt and peck typist", so it'll be interesting to see how this gets on. Besides using the keyboard with the UMPC, I plan to use it with my (hopefully soon to be resurrected) iPaq hx4700 Pocket PC.
This is what a Righty FrogPad looks like (if you click on the image, you should see a life-size version). I bought the Lefty version, in white, with the intention that this would leave my right hand free for mouse or stylus use.
Physically, the unit seems pretty robust, with a slide on cover. It comes with a CD with a typing tutor (for Windows and Mac, but the Windows version seems to work OK on Linux under Wine), a retractable USB power cord and mains adaptor, and several leaflets and manuals.