Here's a simple, relatively cheap, not-physically-attractive way to backup your computer:
1. Get one of these gadgets for as little as $20-25:
http://www.amazon.com/s/ref=nb_sb_n...ords=usb3+sata+dock&rh=i:aps,k:usb3+sata+dock
(many items shown, they all work the same, just pick one you like that's cheap)
2. Download the FREE version of CarbonCopyCloner (version 3.4.7) from here:
http://www.bombich.com/download.html
(disregard the warning about what systems it works with, works fine for me with 10.8)
3. Get one or two "bare" SATA hard drives from the vendor of your choice (or, do you know anyone who has an old drive lying around they don't need anymore?)
Put the drive into the dock, connect it, turn it on, initialize with Disk Utility.
Use CCC to "clone" the contents of your internal to the docked drive.
You now have a "bootable clone" -- a fully bootable backup of your main drive. If you need something from it, just connect and it will mount in the Finder, then copy over what you need. You can even "re-clone" the entire backup back to the internal drive if you need to.
If you run off a second cloned copy, keep that somewhere "off-site" (office, bank vault, even a fireproof/waterproof box in your basement). That way, if the house burns down, you'll STILL be backed up.
You can also periodically boot from the docked drive, to do regular maintenance on the internal hard drive.
There is NOTHING you can buy that will beat having a bootable clone backup close-at-hand during a "moment of extreme need". You ALWAYS want to have a second bootable copy of the OS and your data close by.