I've been playing with the HiTechnic Acceleration Sensor. Here you'll see a small program (a modification of a test program HiTechnic created) that outputs the values of the X, Y, and Z axes.

Surveyor info: http://us.mindstorms.lego.com/nxtlog/projectdisplay.aspx?id=2382bc2f-0e69-40f6-a456-5666b615a97d
I'm working on a special little bot now that will use the Acceleration Sensor to keep an object it is holding in a very specific orientation. More on this soon...
You can find more info on the Acceleration Sensor here. HiTechnic will also soon make the NXT-G block available for download soon, so keep your eyes open.