Amazon has the Western Digital WD6401AALS 640 GB Caviar Black SATA 7200 RPM 32 MB Cache Bulk/OEM Desktop Hard Drive for $50 with free shipping.
Technical Details:
* Ships in Certified Frustration-Free Packaging
* WD Caviar Black high performance 3.5-inch SATA hard drives co MBine 7200 RPM spin speed, 32 MB or 64 MB cache, and SATA 3 GB/s interface for the ultimate in power computing.
* High performance electronics architecture features dual processors and bigger, faster caches for maximum read and write speeds.
* StableTrac -- The motor shaft is secured at both ends to reduce system-induced vibration and stabilize platters for accurate tracking, during read and write operations.
* 640 GB capacity holds up to 128,000 digital photos, 160,000 MP3 files, and up to 77 hours of HD video; 5 year limited warranty
Amazon.com: Western Digital 640 GB Caviar Black SATA 7200 RPM 32 MB Cache Bulk/OEM Desktop Hard Drive WD6401AALS: Electronics
Western Digital WD6401AALS 640GB Caviar Black SATA 7200RPM Hard Drive $50 + FS 
