Western Digital Caviar Blue 500GB 7200RPM Internal Hard Drive for $49.99 shipped after promo code EMCYTZT2657. Here is a screenshot for reference. It features 7200 RPM, 16MB cache, and uses SATA 6.0Gb/s interface. Note that it comes in OEM packaging, which means no pretty retail box but is otherwise identical. Most places have this internal hard drive for about $59 or more.