Depending on what interface you want, you have a variety of choices from Other World Computing. I bought one of the basic OWC Neptune FW400 drives mainly for backup, but it is also bootable on my older machine. The newer Intel machines can boot via USB 2, so that might be a good faster option for your MacBook, but they have some OWC Mercury drives that offer multiple interface options, so you have the flexibility of FW400/800 USB2/1.
http://eshop.macsales.com/item/Other%20World%20Computing/MEU7500G16/
http://eshop.macsales.com/
Get two of them, so you can make a regularly scheduled backup, using DejaVu, Retrospect, or CarbonCopyCloner, etc...