Memorex SlimDrive 640GB 2.5″ USB 2.0 Portable Hard Drive for $70.84. Shipping is $0.97 for a total of $71.81 shipped. Here is a screenshot for your reference. It is USB powered and does not require an external power supply. It is smaller than most external hard drives, making it more convenient to carry around. Most places sell this portable external drive for about $99 or more.