I recently discover one of the best backup plugin for WordPress. It is called Backwpup and can be downloaded here:
http://wordpress.org/extend/plugins/backwpup/
Or install directly with WordPress plugin manager. What is fantastic with this backup tool is the fact it integrates with the major file sharing services like Dropbox, Rackspace Cloud or Amazon S3. Also you can schedule the backup of the database and files so you don’t have to worry anymore about doing this manually.
Give it a shot!