Newegg has the Western Digital Caviar 640GB 7200 RPM 16MB Cache SATA II OEM Hard Drive for $90 - $5 (with code EMCAHCFAD) = $85 with free shipping

List Price: $89.99
Mail in rebate /Discount: - $5 (code EMCAHCFAD)
Sales price: $85 with free shipping
Price After Rebate: $ N/A

Technical Details:
Model
Brand Western Digital
Series Caviar SE16
Model WD6400AAKS
Performance
Interface SATA 3.0Gb/s
Capacity 640GB
RPM 7200 RPM
Cache 16MB
Physical Spec
Form Factor 3.5"
Manufacturer Warranty
Parts 3 years limited
Labor 3 years limited

Link to the buy: Newegg.com
Rebate form: N/A