I like to maintain multiple backups of the data that is most important to me. I use Time Machine as the primary method of ensuring that all of my data is backed up. While Time Machine is reliable, I like to take it a step further by creating a secondary backup of key data whose loss would cause me a good deal of grief. Files can become corrupt, get erased accidentally, or be stored on a drive that fails.
Courtesy of Apple
One of the items I treat with this extra precaution is my iTunes library. Like many of you, I have a large collection of music. Some of the tunes are irreplaceable because they come from live recordings I made oh-so-many years ago.
Once a month, I back up my iTunes library to a separate drive dedicated to non-Time Machine backups. You can back up your files on any schedule that suits you; once a month works fine for me, and is easy to remember. I also use Time Machine to perform regular backups every day.
The process of backing up an iTunes library is fairly straightforward, but the restore mechanism is a bit tricky. You won't find a restore command in iTunes itself, but with the help of a keyboard shortcut, your restored library will be ready for use.
You may also want to consider a separate backup of your iPhoto library. More than likely, it contains a number of precious images that you would not want to lose.