I just put a Western Digital Scorpio Black 320GB 7200RPM in my laptop. I noticed a definite performance increase over the old 5400 RPM drive.
$75.99 (w/o "Free Fall")
http://accessories.us.dell.com/sna/p...9&sku=A1727967
$89.99 (with Free Fall)
http://accessories.us.dell.com/sna/p...9&sku=A2387329