At the beginning of last year I bought a USB black frogpad, and several months ago I bought a Matias half-keyboard. Both are similar in size to the N800 and either should work nicely as a portable external keyboard. I find the half-keyboard easier to use for normal typing, but symbols and special functions are hidden in the mode key. For programming or text entry including lots of symbols the frogpad wins - the keys are clearly labeled and symbols are easier to access. The black frogpads have better firmware than the earlier models, but last year the only place I could find them new was at ThinkGeek. The half-keyboard was difficult to find as well, but they seem to be available at more sites?

half-keyboard site
frogpad site (looks like they have black in stock again?)

Until my host cable gets here I'm using my old bluetooth frogpad. It was easy to pair, but I've already had it freak out once and it doesn't work as well as the new models.