They recently put out a new version of Jungle Disk, and I have to sing its praises again.
Since this version hit, and as a JD+ subscriber, my server backups are only sending up the changed parts of the files. The database backup files change about a total of a half-gig every night, which is a lot cheaper to upload than the full five gigs. So now, between my home stuff (photos, docs, MP3's, some video), and the server backups, I'm now storing over 100 gigs of data on Amazon S3. Monthly cost? Under $20.
With this new version, they also have an option to use Rackspace as the cloud storage (JD was bought by Rackspace), and it's less expensive and doesn't charge the bandwidth fees that S3 does. Certainly I'll think about it to cut some expenses, but I'm not sure it's even worth messing with. I know S3 is insanely redundant with Amazon's absurd infrastructure, but I don't know that Rackspace can deliver the same thing. It's hard to say.
Either way... fantastic product. Between Time Machine backing up our three Macs at home and the cloud storage, I feel pretty good about our backups. Backups only really work if you don't have to ever think about them.