Seagate Barracuda 500GB 7200RPM Drive for $39.99 shipped after code ZZF1022 and a $15 rebate.  Here is a screenshot before the $15 rebate for your reference.  Note that it is in OEM packaging, which means no pretty retail box and marketing materials.  It may be interesting to know this is the 7200.12 model, which utilizes a 500GB/platter design, the highest density currently available for reduced power consumption and better performance.  Most places have this drive for about $54.