Automattic (the developers behind WordPress) have released VaultPress and it may just amount to the best security and backup solution for WordPress available.
According to the formal announcement from Matt Mullenweg, "The vision of VaultPress is to ensure that blogs and sites under its care are always completely secure, regardless of what happens. Today, this means every bit of content will be safe, from plugins and themes to the smallest comment or post revision, with WordPress-aware, real-time, multi-cloud backups. This is some of the most advanced technology I’ve seen interact with WordPress."
Keep in mind that this is much more than just a plugin to create backups. The product aims to guard your site again dangerous and fraudulent activity through real-time and continuous monitoring - even updating fixes automatically. Interested users can sign up for VaultPress in private beta.