Depending on the usage. If you want a portable one, buy a Hitachi Travelstar. If you want a bigger capacity one that just sits on your desk, by a Hitachi Deskstar. Then buy an enclosure (make sure you buy the right one, depending on the physical size of the hard drive you buy) for $10 on ebay to put the drive in.
I was looking for about a 500gb one...I think I found the one I want to buy...Waste was so helpful, he gave me a whole list of brands to buy! Thank you too Henry!