I got the USB version of the silver Seagate Freeagent Go portable drive (500gig) for $119 at Staples on sale - noticed it was even cheaper last week at Newegg. I was comparing it to the WD Passport 500gig at the same price, and liked the form factor of the Freeagent better (the silver one matches my MBP.) I only use it for cloning/backup of my internal hd, so it's not connected that often - just for daily backups. It came with a nice case it slips into and is much more stylish than the WD, in my opinion. I do have a WD 500gig internal, so I'm not playing favorites.
The Freeagent Go 500gig drive is really quiet, and while it's not blazingly fast connected through the usb port, it does it's job very handily. Bus powered, only 1 usb port required.
Also... I forgot - when I bought mine (Seagate Freeagent Go) they included the optional usb dock for free. I tried it, but really don't think it is terribly useful. But, it was nice to have it for free.
Anyway, that's just some feedback from someone who had to consider the options myself a few months ago.