Laptop security devices?

Does anyone have any inormation or experiences with security devices for Laptops?

I am particularly interested in devices such as USB keys or PCMCIA cards (or any variation on the theme) that will stop the laptop from being booted or logged on orsimilar. I have heard of “biorhythm” (fingerprint?) devices and would be interested in info on these too.

I am aware of the Microsoft Windows (NT, 200, XP) EFS, and while that offers protection to data, I would like to also look at methods that provide protection for the whole system