You might want to take a look at the WD PiDrive.
It’s specially designed to work with the Raspberry Pi. More importantly, have a look at the cable that comes with it.
Here’s some more information:
http://support.wdc.com/KnowledgeBase/answer.aspx?ID=12968
EDIT: I don’t know if the cable will work with a Passport or not (it’s designed for the PiDrive, but the drive does use a USB interface…), but it looks like the cable is being sold standalone now:
