I'm not sure just how practical or pertinent this is to anyone, but I came across it this morning while looking into something else and just couldn't resist posting about it. Thanks to USB host mode and a bit of creativity all of these devices should work with the ITs:

http://www.phidgets.com/index.php

There's full open-source drivers/API, but even cooler, there's also now a python library available as well... so theoretically you could start using one of these without even needing to compile anything for the ITs... At the moment even at 1.2" square I think the accelerometer might be a bit large, but there are lots of other creative people on here who might be able to think of unique applications...

(off the top of my head, what about taking one of those touch/slide sensors and mounting it under the back battery cover; then rig up some software so anytime you want to, I don't know, say change the volume or something, you just slide your finger along the back of the N800?....)