I puchased an MSI BK100 from deal extreme. It just came in the mail today and seems to work pretty well with my Diablo n810. A few notes in case you're thinking of picking one of them up (they're cheap):
* It comes with a little printed documentation booklet, but it's entirely in Chinese. Don't buy if you really want proper documentation
* The driver CD that comes with it also contains only Chinese documentation
* I've only used it for a few minutes, but the speed at which the characters appear on the "Notes" application seems a bit slow; ie. I type very fast, and sometimes chunks of words will appear on the screen, whereas on my laptop, I can't possibly type fast enough to not see each character appear independently
* That said, the keyboard is reliable, in that it doesn't lose any characters

I mostly followed these instructions to get it to work, but with a few caveats. When I typed "hcitool scan", it wasn't found. Use "./btkbd scan" instead to find the address. In the config file, modify BDADDR according to what the scan revealed. Uncomment the KBTYPE option, but don't change it's value. Everything else in the instructions is correct.