[DL.]

Smaller amounts of data that are frequently updated can be backed up to rewritable media such as DVD+/-RW or DVD-RAM. DVD-RAM is very simple to use, works like an external HD or a floppy (just copy the files to the disk in your file manager or script it). The problem with it is (just like any DVD) the limited storage space available, and the fact that it's very hard to find fast media (I haven't been able to find any higher speed than 5x, even if 12x is supposed to exist).w

Backup media for normal people (=no expensive tapedrives) haven't managed to keep up with the size of HDD:s.
Unfortunately in a few years when the prices for HD-DVD or Blue-Ray has come down we might still have similar problems as we have today with limited backup space.

Online backup is not an option for many GB:s of data when upload speeds are less than a MB/s, even if you got one of those 100Mbit Fibre-LAN connections (widely available here in Sweden) it would take quite some time to upload hundreds of GB:s.

Using a combination of DVD:s and HDD:s (maybe with RAID) is the way to go at the present time.

A separate backup-server or a NAS with RAID:ed (level 1 or more, maybe nested) disks might be a good choice. Cloning it regularly to one or more other disks which are kept at a safe location (=off-site) will give you more than enough (probably overkill) storage safety. You got to have very bad luck if a solution like that would fail. The price of such a solution (500GB, 2-disks in RAID1 NAS+1 extra disk) starts at about 800$ (may differ a bit), it's not cheap but what is? This may not be the solution for the thread starter (the price may be too high) but others may find a solution like that suitable for their needs.