I searched long and hard and found a GREAT solution.
Archive Creator allows you to write to CD/DVD, it spans disks as necessary, and includes a web-gallery style index that can go on just the first disk in the set, or all of them. You browse through the folders to find the image you want, then click a button to open it. It prompts you for the appropriate disk in the set. This allows you to just recover one image if you want to.
Spanning disks was the biggest feature that I wanted. Using any other backup software meant that you had to restore the whole set (say using Windows backup) or go through the tedium of breaking-up images into 700Mb chunks (say Nero). This has been a real life saver for me.
I burn a CD when I'm done shooting with the model and have done no editing. Then when I'm done editing I burn another CD and store that off-site. And occasionally I copy the images over to another HD on a different PC, just to be sure.