Newegg has the Western Digital Caviar Green WD6400AACS 640GB 7200 RPM 16MB Cache SATA 3.0Gb/s 3.5" Internal Hard Drive for $50 with free shipping.
Details:
* Cache: 16MB
* Average Seek Time: 8.9ms
* Features: Reduced power consumption - WD has reduced power consumption by up to 40 percent compared to standard desktop drives with the combination of WD's IntelliSeek, NoTouch, and IntelliPower technologies IntelliPower - A fine-tuned balance of spin speed, transfer rate and caching algorithms designed to deliver both significant power savings and solid
* Parts: 3 years limited
* Labor: 3 years limited
* Model #: WD6400AACS
Newegg.com - Western Digital Caviar Green WD6400AACS 640GB 7200 RPM 16MB Cache SATA 3.0Gb/s 3.5" Internal Hard Drive -Bare Drive
Western Digital Caviar Green WD6400AACS 640GB 7200RPM SATA Hard Drive $50 + FS 
