I've been a data "hound" for the last 20 years and that data takes storage space. I've gone through a series of external hard drives, which succeded each other as capacities rose and prices came down. But when I purchased my Macbook Pro, I realised that I would need an external drive that did not require an external power adapter (well, to be precise, I did not NEED, but did think it would be more convenient to be able to carry just a drive and adapter cable, rather than a drive, adapter cable, AC adapter and power cable). I had shopped around a little bit and settled on the Western Digital Passport Studio 500GB drive. The clincher for me was the USB2.0/Firewire 400/800 connection options.
So far, I've found the drive both fast and quiet, which are obviously features that are desirable in a portable drive. I was also quite impressed that WD would include all three connection cables within the box (USB 2, Firewire 400 and Firewire 800). It has exceeded my expectations, except for one: total capacity. I would replace this drive in a second if it was available in a 1TB format, instead of the current maximum of 640GB.