As the previous poster mentioned, OWC is good, I haven’t owned one but every professional project or professional company I’ve worked for has used OWC with good results. I’ve had good luck with Maxtor brand drives. I’ve had a 200 GB for years with no problems, and just recently bought a 750 GB for only $150 — they seem to be pretty affordable. Not to say you should base your purchase on price, but like I said, they seem to be quality drives as well as being affordable. I would stay away from LaCie — just heard too many bad things about them crashing.
As for what kind of drive to get, USB vs. Firewire, etc. I would recommend Firewire for FCP stuff. My original Maxtor was a USB and it wasn’t terribly slow, but FW is a little faster and it’s always nice to have the top of the line when you buy a drive. Keep in mind that the 15in Macbook Pro only has one Firewire 400 port (at least mine does — dont know if they changed that) so if you get a drive with only Firewire 400, as I did, you won’t have a port for plugging in a FW deck or camera or anything else at the same time unless you get a FW hub. Just something to keep in mind. I believe the 17in Macbook Pro has at least 2 400 ports.