s3fs is a fuse filesystem that allows you to mount an Amazon S3 bucket as a local filesystem. It stores files natively and transparently in S3 (i.e., you can use other programs to access the same files). Maximum file size=5G.
"Recently, I have started backing up my servers to Amazon S3 (Simple Storage Service) using Duplicity. So far, I am pleased with the process and the costs involved. I still do regular disk dumps to my own backup server but may slowly phase down the frequency of these dumps."
"Duplicity backs directories by producing encrypted tar-format volumes and uploading them to a remote or local file server. Because duplicity uses librsync, the incremental archives are space efficient and only record the parts of files that have changed since the last backup. Because duplicity uses GnuPG to encrypt and/or sign these archives, they will be safe from spying and/or modification by the server."