Video from Vimeo. Click link for iPad/iPhone version.
We can now add "entire separate computer" to the list of working keyboards, as the video above demonstrates. Eolake Stobblehouse (who was the benefactor behind TidBITS' staff getting iPads) figured out that his Alphasmart Neo behaves just like a powered external keyboard when connected to the iPad. The Neo is the spiritual descendant of one of the original 'tablet' computers, the legendary Tandy Model 100 series. A week's worth of battery life on a few AA batteries! Those were the days.
Granted, it may seem a bit weird to carry a second machine along just to type into your tablet, but to each their own. Now, if we could get an import utility that would take text files from the Neo and put them on the iPad... Update: Thanks to commenters who point out that the Neo's 'Send' function will work with any iPad app that supports text input.
Direct link to the video for iPhone/iPad is here. This video (not produced by us) is hosted on Vimeo, which supports HTML5 playback on their site but does not support embedding.
Thanks to Peter for the tip.