Samsung EcoGreen F2 HD502HI 500GB SATA Internal Hard Drive for $39.99 shipped after this $10 rebate.  Here is a screenshot for your reference.  Note that it comes in OEM packaging, which means no pretty retail box but is otherwise identical.  This is a 5400rpm drive designed to be energy-efficient instead of maximum speed, which makes it a more appropriate storage drive than a boot drive.  Most places have it for over $60.