Does it have to be "portable" as in 2.5" HDD? If not, I always like to build my own. I like the Macally External cases with Seagate Barracuda drives.
Macally also makes 2.5" enclosures, but they don't look as slick as the MyBook, FreeAgent, and Passport OEM drives.
I have lots of Macally cases in many flavors. I just bought a 2.5" enclosure (PHR-S250CC) with a SATA interface and USB/FW ports. Works great.