You GOTTA have firewire? Why not something eSATA? If you have a desktop, you can grab an eSATA PCI/PCIexpress/whatever card for cheap, and spend the rest on anything with good reviews from newegg.com .... That's the route I took, I now have a few TBs. Got a $40 dock, and now each 1TB drive is only 80 bucks!
I'd definitely go eSATA if you can. FireWire is generally okay with most audio apps, but I've run into some audio apps that go ballistic because they don't request audio data far enough ahead of time to accommodate the somewhat higher request latency inherent in FireWire. (USB would, of course, be a thousand times worse for those apps....) With eSATA, you can essentially consider it equivalent to having another internal HD.
Either way, my recommendation for audio purposes would be to either buy a case from a vendor that tells what FW-ATA bridge chipset they use or to buy a case and build it yourself. It's usually not much cheaper, but it puts you in control of the silicon.
My advice would be to go with an Oxford bridge chipset. That's generally considered the gold standard. Some of the other bridge chipsets seriously suck. That said, the worst FireWire to ATA bridge chipsets are still much, much less buggy than the worst USB to ATA bridges (so long as you don't send the magic series of commands that made some of the Oxford 912 chipsets with early firmware revisions wipe the hard drive). At least the FireWire chips all support flushing buffers to disk, AFAIK. By contrast, there are certain USB chipsets that IIRC almost guarantee data loss....