In the event of a hard drive crash---or simply to make your data more portable---it's advisable to have a portable storage device, such as an external hard drive, a USB flash drive or a memory card on hand. While each of these options ultimately serves its intended purpose, so too does each come along with a number of advantages and disadvantages.
External Hard Drives
Among the advantages of an external hard drive is its storage capability. As of August 2010, consumer models of up to eight terabytes are available (a terabyte being equal to 1,000 gigabytes). Even if you're not going for mega-storage, however, you should be prepared to pay at least £32 per unit. External hard drives are durable, with metal casings built around their inner components. Of course, this sturdy construction can also make them heavy and large---and inconvenient to transport.
USB Memory Sticks
Also known as "flash" drives, USB memory sticks plug directly into your computer's USB drive and are pocket-sized. Additionally, a USB memory stick comes with a "cap" to protect its sensitive insertion hardware, so you can avoid damage without any auxiliary container. Capacity, while below that of an external hard drive, extends from 1GB all the way up to the mammoth 256GB model as of August 2010. All this being said, a USB flash drive probably isn't going to survive if you step on it or drop it from a high window. Thankfully, replacing it won't break your bank--models with minimal, 4GB capacity can run under £6 as of August 2010.
In early 2010, the Silicon Power company released the World's first 128GB flash memory card. Although these and popular "SD" memory cards are usually intended for cameras and mobile devices, it's perfectly feasible to store other files---such as music and documents---on them. As is the case with USB flash drives, memory cards can be had for under £6 as of August 2010 and are extremely portable. The downside is that not all computers have memory card readers, which means you may have to purchase an adaptor in order to be able to use one. While extremely small and therefore portable, you must carry your memory card in a case or sheathe to protect it, and even then, its flimsy construction might not stand up to even the most minor of mishaps.