I'd like to encrypt my system disk and use a keyfile stored on a USB flash. I was planning to use truecrypt, but it doesn't support keyfiles for system drive encryption.
Our company laptops are encrypted with Truecrypt and you have to use a USB key called a Yubikey to 'unlock' them.
The keys 'type in' a 32-character string/passcode when the sensor is pressed. Very simple to setup.