Another distinction between Firewire and USB: USB is handled by the driver (read cpu/memory/latency/...) while the controller handles most of the load for Firewire, saving resources for other critical work.
Most benchmarks talk about bandwidth numbers, someone should compare cpu loads during those transfers...
Spirit - I personally went a cheapskate route and bought a generic Firewire IDE enclosure and put a 120gb drive inside. Works great, although it could probably be better. Some of the Lacie ones are nice, although a little more expensive. If money is no object, Glyph makes nice stuff too.
Imho it's a good tip from dArKr3zIn to go with some generic enclosure and put your favourite disk in.
I don't know of any 'native' firewire controlled drives, they all use IDE to FW boards
