Currently that would be the Samsung Spinpoint F3 - ( http://www.newegg.com/Product/Product.aspx?Item=N82E168... ) - It is one of the few drives with a single 500GB platter which means fewer Heads needed so it is quieter and faster than most other 7200RPM drives and at only $54 it is a much better buy so you might as well get 500GB instead of 150-300GB since the cost is pretty much the same !! (figure the cheapest 160GB is going to run about $45 shipped so the extra $10 is worth it for the added storage and faster drive.
Data will be much more condensed on a hard drive with a single platter vs. one with multiple platters. The drive will only be able to read off of one head at a time. For that reason, the drive is quicker, as the head is reading more data per second.