A while back, I wrote about the Macintosh program Seismac that would use the sudden motion sensor in your computer (you know, in case you knock your Mac off the table, to stop the hard drive) to display a 3-axis accelerogram. It is a great teaching aid.
My IT colleague Teb not only relieved me of some candy this weekend (with his kids), but he told me that this capability is now available for Macs as a "widget" (a little snippet of software).
You can download it from Apple. Free, only 141k.
System requirements - Mac OS X 10.4 or later; Macbook, Powerbook or iBook