I have used Jungle Disk together with Amazon S3 with great success. Jungle Disk is an application that you install locally, which proxies cloud storage, and creates a virtual WebDAV disk-drive on your PC. It supports Amazon S3 US & EU and Rackspace Cloud Files as storage backends.
Additionally, Jungle Disk has a built-in backup function, with which you can tell it to automatically back up specific directories. The backup functionality isn't super slick, but it gets the job done.
Jungle Disk has a great feature on S3. They have deployed their own servers on Amazons EC2 compute grid, and use these servers as proxies to the S3 storage. The benefit is that uploads can be resumed, and uploads use more than one TCP/IP stream which gives much higher upload speeds. When I used this (more than a year ago), it was a separate subscription. Now I don't see it mentioned on their site; maybe it has been included in the standard Jungle Disk product, or maybe something else has happened. You might want to investigate the current status of this feature.
All in all I was very happy with Jungle Disk + S3, but eventually I left. S3 is priced well, but it's still too expensive for me, as I regularly back up 600 GB of data now. The price of S3 for larger amounts of data is the sole reason why I stopped using Jungle Disk + S3. For just 30 GB data it will be great.
I'm currently using Mozy, and I'm evaluating BackBlaze. I haven't found the ideal online backup yet, unfortunately. Mozy is cheap and nice, but upload is too slow (~0.75 Mbit/s effective from Scandinavia). BackBlaze is faster, but has certain file restrictions that I'm unhappy with (does not back up .ISO files, virtual machine disk images, or files larger than 4GB).