No matter how you backup your data there is always the risk that the backup fails. In the time, from either your main copy or your backup has failed, only one copy of your data exists. If the other copy also is lost you have lost your data dispite of backup.
For this reason many copies of your most important data might be worth while.
Burnable DVDs are good for this, because they are cheap and can only be written once anyway. Select your most important data, so you can pretty much fill one or maby more DVDs.
One way of storing these DVDs are to put the newsest in a place outside of your house where you come often. That might be at work or at a friends house. When you visit some far away friends or family, bring one of the older DVDs and have it stored there.
Then, in the worst case you might not have all of the newest data, but you have most of your important data. And it is done for very little money.