In your ~/iTunes folder is the actual library that should only be a few hundred meg at best based on the size of your overall music library.
Mine is 443.13GB. I use a 1TB RAID 0 (2x500GB) for my main music drive, a striped RAID 1 (2x1TB) for my first backup, and a 1TB single drive as my redundant backup. Super Duper keeps everything synchronized. This scheme has saved me a couple of times over the years. Hard drives will fail, and only a good backup plan will protect your data.
If you have a small iTunes collection the DVD idea will work, but keep in mind that every time you add something to iTunes your backups are now obsolete. Yes, you can sort by date and back up only your recent additions, but how often do you want to do that and how many DVDs are you willing to keep cataloged and sorted? Also realize that having only one backup on any medium is not a good idea. You'll need two copies of each DVD for safety.
Using a hard drive as your backup is inexpensive and painless. You can use Carbon Copy Cloner (free) or Super Duper (cheap) to automate your backups, and you will always have a current copy (or preferably two) of your iTunes library.