nothing specifically for mp3s. Its tricky, cause you can't easily set up a regular backup of selected folders, if the mp3s are likely to grow.
Assuming you have your mp3s in folders by artist, you could spend a few minutes checking each folder size, and then how many would fit on a DVD - allow a good amount of space (like 25%) for future growth, thent set up backup jobs for each group - Nero has a backup program and you can kick them off manually. It also stores them on DVD in a way that you can just browse by explorer - no fancy encryption.
If you don't have your mp3s organised - get them organised. Use iTunes if you need to, or a tag editor like 'Tag&rename', which can create a folder/filename structure based on the id3 tags (and vice versa). I used that and got my files sorted pretty quickly (although because I now use iTunes, I have them in iTunes order, which is also by artist)
