Any of the top 4 (Maxtor, Seagate, IBM, Western Digital)
5,400rpm are slighly cheaper and fine for backup use but if you intend possibly to use as the main drive at some point , the extra few bucks for a faster 7,200rpm drive would be worth it.
Avoid refurbished or non descript brands.
Martin Replying helps further our knowledge, without comment leaves us wondering.