If you're like most people, you're probably running your computer without a backup of all your important stuff. If there's anything in your hard disk(s) that you don't want to lose, now might be a good time to consider available backup options. You never know when that new disk drive will give way.
With storage hardware getting cheaper all the time, it's not that hard to get an extra hard disk for backup purposes.
There's lots of options off- and online. Here's just a few:
Hard disk - Nothing like good ol' traditional hard disks for backups. They're cheap and getting cheaper all the time. Getting Terabytes of storage isn't too far-fetched these days. You can get them in USB enclosures, or even as NAS devices. SSDs are still much too expensive; you'll more likely want that as your running disk drive instead of a backup.
Online backup - With free storage available online, you might not even need to get any extra storage device at all. Dropbox gives you 2GB free online storage to start with, and you can pay for more as needed. The best part is it works on all major OS platforms. Ubuntu users could also opt for Ubuntu One. Like Dropbox you start with 2GB free and can pay for more as and when needed.
CDs, DVDs, Blue-ray - If you don't have massive amounts of data to keep, then optical storage might be a good option too. For larger amounts of data, a hard disk might be a better option.
Solid state storage - USB keys are small and convenient storage devices. They're also not all that expensive these days. Easy to use, easy to keep. That's always a plus.
Most people don't backup because it's a hassle. But consider what happens when you lose all that data. Will you be able to get it back easily? Or, at all? How badly will you miss it? It's fine if you don't mind losing it.
The choice is yours.