I use both CDRs and a hard disk on a second networked machine. I also use a USB pen drive for the relatively small amount of absolutely vital data as a third line. Stopped using a DAT drive (only 2Gb and too slow).
Trouble is whatever you use, the media has the potential to go belly up on you, that's why I have a belt and braces approach and back most things up to at least two different places.
You could use some of your ISP's free webspace, and upload some to that, they will keep backups on a regular basis so that should solve part of the problem. Multiple pay as you go dial up ISPs to increase your free web space? You would probably only have to dial in once a month to keep the account active, therefore it's a cheap option.