One thing to consider is "incremental backup".
If you have thousands of songs or pictures on your computer it does not make sense to back them ALL up to CD or DVD each time you do a backup.
If you did you would have loads of CDs or DVDs with the same data on them.
But you may have downloaded some NEW songs, or got some NEW pictures, and you want to back them up, but picking out he new songs or new pictures to backup may be difficult.
Incremental backup is backing up ONLY those things that are new, or have changed, since the last back up.
You can buy software programs that help you manage your backups, such as Acronis True Image.
I have to be honest and say I have never used any of them as I manage my own backups, but it may work for you.
More here:
http://eu.acronis.com/homecomputing/products/t rueimage/