Lifehacker reader rocky.colt.tumtum has built a Raspberry Pi-powered portable PC, complete with multiple USB ports and a 2TB drive. He's also documented his build process, and shown you how you can build one of your own.
He outlined the entire process over at Instructables, along with all of the parts and components you'll need to make the whole thing work. The finished product is a slightly-bigger-than-palm-sized complete computer, with a Raspberry Pi at its heart. The build has enough ventilation to keep everything inside cool, a USB hub, a 2TB external hard drive, and an external reset switch. He calls it Mjölnir, and we can't blame him.
He used a simple die-cast aluminium electronics enclosure for the outside, an off-the-shelf hard drive, and basic cables and connectors. You'll definitely need your soldering iron and drill for this build, but when you're finished, you'll have a portable PC you can use for anything and that can go anywhere with you. He uses his as a go-anywhere media centre. Hit the link below for the full walkthrough.
Mjölnir - The Portable Media Computer [Instructables]