CD Creator is a nifty little tool that helps you to fill CD-Rs to the maximum. CD Creator can calculate optimum files and folders in order to make best use of the disc capacity. After the calculation process you can move these files/folders to another directory and then burn them. You can also pick files manually and CD Creator will show which files can still be fitted to the CD-R. Supports any media size, so might be useful for other than CD-R backups too.

Very useful if you have large amount of data to be written on CD-Rs, like MP3 collections for example. I have tested a couple of this kind of applications and CD Creator seems to be the best so far.