WP S3 Backups

Using this plugin, you can easily and automatically backup important parts of
your WordPress install to Amazon S3. Amazon S3 is an extremely cheap service
that is easy to set up. For pennies a month, you can make sure that your
important files will be kept safe.

Important caveat: this plugin currently has to be run on a linux server.
Also, the wp-content/uploads folder has to be server-writable or it won’t be
able to create the zips for backup.