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I've found really good prices before at zipzoomfly.com

This was back in my PC days, but dealing with them was always good.
 
Try newegg. Their prices were cheaper on the HD is was looking for but i did not order from them as 1) they were out of stock on the HD i wanted, and 2) they do not have a phone number for placing orders. With my billing and shipping addresses constantly changing/being different, it is nice just to talk to someone in via the phone, rather than try to figure out some websites cryptic forms.
 
Be careful you get a drive with the full written manufacturer's warranty, Maxtors should be 3 years and Seagates 5 years. The cheapest vendors are selling non-retail authorized "pulls" and OEM drives with none or 1 year warranty.
 
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