mwave offers the OEM Western Digital Caviar Blue 500GB Serial ATA 6Gb/s 3.5″ Internal Hard Drive, model no. WD5000AAKX, for $39.99 with free shipping ($0.08/GB). That’s the lowest total price we could find by $5, although we saw it for $15 less in May. This drive runs at 7200 rpm and features a 16MB cache.