UBestDeals via Amazon offers the OEM Western Digital Blue 500GB Serial ATA 6Gb/s 2.5" Internal Hard Drive, model no. WD5000LPVX, for $38.99 with free shipping. (Newegg has it for a buck more via "ESCATNN23".) That's $3 under our January mention and the lowest total price we could find by $6. This drive runs at 5400 rpm and features an 8MB cache.