Today only, Best Buy via eBay offers the Western Digital Blue Series 750GB Serial ATA 6Gbps 2.5" Internal Notebook Hard Drive, model no. WD7500BPVX, for $43.99 with free shipping. (Amazon charges the same.) That's a buck under our mention from last fall and the lowest total price we've seen. (It's also a current low by $5, outside of the mention below.) It features an 8MB cache and runs at 5400 rpm.
Of note, for new customers only, Jet offers it for $32.07 via coupon code "15BUCKSNOW" with free shipping. Plus, score additional discounts at checkout.