The Aegis Padlock Secure Drive has its own keypad and admin feature to lock your data down. It also has 128-bit realtime or 256-bit AES hardware encryption, shock mounting, and come in sizes up to 500GB.
The Mercury-On-The-Go from OWC is a somewhat tempting three-way connectible 500GB portable HDD. Component-wise there are no surprises, under the hood is a 2.5" 5400 RPM Hitachi Travelstar 5K500 with an 8MB cache. With Firewire 400/800 and USB 2.0 you get three-way connectivity and bus power.