When I was starting this site I was looking for a reliable solution to backup the site. I have been looking bit around and found this excellent plugin for WordPress:
BackWPup

This plugin is absolutely awesome, with many features, just mentioning few key ones:

• You can create backup job, where you can define what tables and what files will be backed up – thus you can basically backup all site, or selectively just critical data
• You can store backup file to many locations: locally, to remote server or to many popular cloud services (Amazon S3, DropBox …) – so the backup  available even when site is completely down.
• You can schedule backups with any periodicity  (cron like scheduler) – you can also  run it manually
• It works well even in limited hosting environments