FireWire is a high-speed bus invented by
Apple, but is being adopted throughout the industry as a standard for digital video and audio applications. It also goes by the name of IEEE 1394, i.Link (Sony) and maybe a couple of others. However, the 1394 Trade Association is now really pushing the FireWire brand name.
If you're going with a do-it-yourself FireWire enclosure and drive, make sure you get an enclosure that has the Oxford 911 chipset, which is supposedly the fastest of the ones available. And for host adapters, go for cards that have a Texas Instruments controller chip.
On the hard drive side, also make sure you get a 7200 RPM drive with a nice big cache onboard.