Western Digital Caviar Blue 640GB 16MB Cache Interal Hard Drive for $59.99 Shipped

Western Digital Caviar 640GB 16MB SATA Hard Drive for $59.99 shipped.  Here is a screenshot for your reference.  It uses a high-density 2-platter design for better performance while reducing power usage.  Note that it comes in OEM packaging, which means no pretty retail box and marketing materials but is otherwise identical.