You're basically going to want the cheapest drive you can find at the capacity you want from Western Digital, Seagate, Hitachi, or Samsung. Ideally you're looking for 7200RPM but if you're mainly just storing files (i.e. you're not running applications or an operating system off of the large drive) then a "green" drive at 5400RPM is fine if it's a good deal. Before the great flood of 2011 I recommended the Samsung Spinpoint F3, but prices fluctuate so often these days that if you find a good deal you should jump on it.
I avoid WD drives because they tend to be kind of loud, but they also tend to be overpriced. If I had to buy one today it would be a Hitachi - they've been the lowest price for a couple weeks now.
($120) Hitachi 7200RPM 1TB: http://www.newegg.com/Product/Product.aspx?Item=N82E16822145533
($80) Hitachi 7200RPM 500GB: http://www.newegg.com/Product/Product.aspx?Item=N82E16822145299
If you want a more "popular" option that has been around for a while, Seagate has a good 1TB option for only $5 more. Some people (not including me) have a negative opinion of Hitachi but I don't think I've heard anyone say anything bad about Seagate.
($125) Seagate 7200RPM 1TB: http://www.newegg.com/Product/Product.aspx?Item=N82E16822148697