Newegg has this Western Digital 300GB VelociRaptor 10k Serial ATA 6Gb/s 3.5" Internal Hard Drive for $69.99 after instant savings.
It's actually a 2.5" drive encased in a larger heatsink that fits into a standard 3.5" drive bay. It operates at 10,000 rpm and features a 32MB cache. The same item sells for $142.99 at Adorama
. Shipping is free.