http://mozy.com/
It's pretty cheap for personal use. For business use it's a lot more.....
There is also Amzazon S3 (not cheap, again)
http://aws.amazon.com/s3/
If all you want to back up are TIF and Jpeg files then
smugmug or
zenfolio are also a viable option for dirt cheap.
There is also
DreamHost who will not only host your website but allow rsyncing 50GB of backup data with their hosting plan ($0.10 per GB per month over 50GB)
gtakacs added 0 Minutes and 50 Seconds later...Double Post Merged Below
FWIW I use a Raid5 NAS that I sync to an external USB drive every week that I keep at my office and I pay no storage fee.