If you're looking for a pure hardware solution, consider looking at Apricorn drives. I have a 500gb portable drive, with AES-256 encryption and a numeric keypad to enter a pin number. The drive won't mount unless the pin is entered and even if the drive is removed from the enclosure, it's encrypted, so data recovery is virtually impossible. I'm using mine for Time Machine backups, and I love it. I work in an environment that requires full disk encryption of both internal and external drives, and it's been one of the easiest drives to work with that we've tried. No additional driver software required. The 640gb (current base model I believe) is around $130.