I've been using Arq for a little while now (former Mozy user) and can recommend it. Arq is substantially better than some of the other S3 backed storage solutio

I've been using Arq for a little while now (former Mozy user) and can recommend it. Arq is substantially better than some of the other S3 backed storage solutions as it takes steps to minimize S3 traffic, keeps incremental backups of recently changed files (ala Apple Timemachine), and an open sourced (Github) restore client in case they go out of business and you need to restore your files. If you're worried about cost, you can also use their Reduced Redundancy storage which would save you a chunk out of that.