AVG, the popular free antivirus product is now offering online backups. AVG's backup system is powered by Carbonite. I've been seeing Carbonite in various installations and my overall impression of it is good. Online backups are worry-free and very easy to use. They're not the fastest in terms of data recovery, but at $50/year it's cheap and worth it. I still recommend an external backup drive for quick recovery, but if you want something completely automatic and never want to worry about filling up your external drive, sign-up for online backup.
AVG's online backup is free for the first 2 Gigs, after that it's $50/year for unlimited space.