Seagate STCA400010 Backup Plus 4TB USB 3.0 External Hard Drive for $119.99 shipped after coupon code B?PVT77SKB?C2J.  Here is a screenshot for your reference.  You get the bragging rights for having the biggest hard drive currently available.  This external drive works with Windows and Mac.  As a comparison, Best Buy currently has it on sale for about $159.