any harddisk from Western Digital, Seagate, Samsung (and Maxtor) is a good one. there are some differences (some offer 5 years warranty instead of 3, some are quieter than others, some are a bit faster) but if you don't care than that is a good one. if you want to learn more, there's a harddisk comparison in tomshardware articles.
The AAKS drives from WD are awesome (i actually have 5 of those in my array). It also depends on what you want thought... The Seagates at 750 and over "7200.11" drives are slightly faster than some others currently