Western Digital Elements 400GB 2.5″ Portable Hard Drive for $79.99. Get a $25 off $75 coupon here or here. Be sure to pick one that is for online use and has instant e-mail delivery. The total comes to $54.99 shipped plus coupon cost. This hard drive does not require a separate power supply and is also smaller than most of them, making it convenient to carry around. Note that availability depends on regional inventory at Staples.