I want to backup my files on iTunes. Can I use CD-Rs to do it? Or do I need to invest in a external hard drive? What CD-Rs would I buy – the 48x or 55x or something else? I have a Mac.
I also recommend having another option handy. As such, I recommend looking into and reading about Dropbox - http://www.dropbox.com
Depending on the size of your iTunes library, you may need to pay to use the service, but it works wonders in an off site back up of your iTunes library (though it has many other uses too if you read up on it more :)). You may also need to move the iTunes library location, but that's quite easy and I'm sure people on this forum can help you if you went this way.
I've done this and it has worked brilliantly. Especially as I'm currently between computers and am unable to use iTunes on Ubuntu Linux on my netbook which is my only computer at the moment. But when I next get a Mac or PC, I will be able to restore my iTunes to what it was before I became between computers using Dropbox and also my back up to my external hard drive :)
I recommend spending money on an external Hard Drive to backup your iTunes Library.
It is way more convenient than burning to CD/DVD all the time [which will also shorten the life of your SuperDrive].
You can get a 250GB Hard Drive for ~50$ which is more than enough space for backups.
Assuming you are running Mac OS X 10.5 or later - with a 250GB (or maybe 500GB) Hard Drive you can use Time Machine to not only backup your iTunes Library but your entire User Profile which includes your settings, Mails, iPhoto Library, Documents, Downloads etc...
Time Machine is one of the best ways to regularly and automatically backup your Mac.
I would go for an external drive as well. It's safer and more convenient than backing up to CD-R's
Its up to you but if you would like
iTunes: Back up your iTunes library by copying to an external hard drive
Backing up your iTunes library to a CD or DVD
you can try CopyTrans TuneSwift