I consider external backup very important and I build my own from an enclosure (with integrated fan) and a good hard disk.
The enclosure I use is Rosewill (USB 2 and eSATA) and the HDDs I use are WD, Seagate, Toshiba. $100 approx. I have four of these external drives operational and the oldest one is about 4 years. Very reliable and very rugged. I like the built-in fan on these enclosures.