You are probably on windows so this post won't help at all, but for mac guys it might. Here's what works well for me.
On my windows machine, I keep nothing of importance. Some movies and games I could download again.
On my mac I have time machine, the built is backup procedure which backs up everything every hour automatically in the background to an external harddrive wirelessly (Apple time capsule). That puts my data on two harddrives, theoretically guarding against HD failure (but no theft/fire where both could disappear or die).
On top of that I backup the very very important data to Amazon S3 (
http://aws.amazon.com/s3/). It is insanely cheap, I think my highest bill has been $1.50 for a month. I use a shell script to back it up but there are a few solutions around for mac to S3.
I found my script here:
http://jeremy.zawodny.com/blog/archives/007641.html and modified it slightly. But if you don't want to fiddle with scripts you can use this service:
http://www.jungledisk.com/