rsnap is a backup and snapshot utility based on rsync. rsnap will not only save the state of your files of the last backup, but it will also retain previous states - as many as you like. This is done in an efficient way, so that only files that have changed will occupy additional space. Even better, as rsnap is a thin wrapper around rsync which adds snapshot rotating and creation, the changes you need to make to your existing backup script are minimal.