Buffalo 160GB MiniStation, TurboUSB Portable Hard Drive. I recently found out that it was nearly full - in fact I have less than 10Gb left.
My wife did some online shopping and came across the TOSHIBA Ultra Slim External USB Hard Disk with a huge 500GB storage on eBay from a company called Highest standard Ultimate (http://www.hsuuk.com). It just cost her £51 including the postage.
It is really compact and comes with a really nice white leather cover. Best of all it is anti shock (from 70cmm height) and has 3 years warranty. Now I want one for myself as well.