Western Digital My Book Premium 500GB USB/FW 400 Ext Hard Drive
WD My Book - quiet and efficient
WD's My Book was worth the purchase.  Small, quiet and fast.  It has two Firewire ports and one USB port and comes with one of each types of cable.  I bought mine so I could back up all my important files from my Mac but I ended up using it to backup the entire contents of my hard drive using the enclosed backup software.  The program was easy to understand and works great on OSX Tiger.  I can't vouch for how it works on a PC, I try not to use them if I don't have to!  The only thing I don't like about the drive is that it can get pretty warm, but that was after an hour or two of backing up my entire hard drive, so that is probably to be expected.  I checked out a bunch of other external firewire drives on Amazon and Apple's websites before I decided on this one and I'm pretty happy with My Book.