Seagate's 4TB portable hard drive requires only USB power
 

Portable hard drives have quickly become the go-to solution for bulk external storage. They plug into just about any PC and offer plentiful capacity for media archives, backups, and the like. Seagate's latest serves up 4TB of capacity—and it's the first to do so with mobile drives that can subsist entirely on USB power.

http://techreport.com/news/25874/sea...only-usb-power