Choose whatever 2.5" or 3.5" size drive you want. Best to get one that has both USB2 and firewire connections. Then go to
www.pelican.com and choose a case to fit it, if you want to protect -just- the hard drive. There is no such thing as a hard drive that is rugged by itself, in the way that a Panasonic Toughbook is rugged. Once you have found the model number of Pelican you want, go to products.google.com and search for it, then buy it. done.