Ian bell wrote:
You might find better prices at ebuyer.com
You may also find that buying the empty caddy and the hard disk separately is cheaper or more flexible as an option. You can get empty caddies on eBay very cheap (and cheerful!), but also places like eBuyer will usually have some aluminium caddies which are very good IMHO.
If you go for a notebook sized hdd (2.5" HDD) the disks are much more expensive but will run from USB power. A 3.5" HDD requires more power than USB can provide so you'll get an external PSU with it. You can also get caddies with firewire options.