http://www.idera.com/productssolutions/serverbackup/serverbackupserviceproviders
They do have a free trial. We use R1Soft pretty extensively. They have had their issues, but they have worked most of them out and it's generally a pretty good product.
The API doc page doesn't seem to show much functionality. I've thought in the past about creating a plugin widget for Blesta, that I could install on my dashboard to show me the status of all servers being backed up, and whether any backups have failed.. but I have no idea if that information is available through their API. Last I checked, their API docs were pretty terrible.