Carbonite is online backup only, so it doesn't really work well for local backups or backups to external drives. You'll still have to handle that yourself. You can try Carbonite for free for 15 days, but after that you'll need to pay up $60/yr to back up one computer with their Home plan, $100/yr to back up one computer with their Home Plus plan, and $150/ur to back up one computer with their Home Premium plan. You can read more about Carbonite's plans and pricing here.
Backblaze earned praise from many of you for being easy to set up, even for non-technical people. It's built for people who want to get their data backed up, without being forced to search for error codes and cryptic status messages whenever something goes wrong. To that point, Backblaze backs up just about everything on your system. You get some control over what's backed up and what isn't, but the point is to be fast, easy, and hands-off, so everything on your system—documents, music, video, external drives you have plugged in, just about anything. Instead of telling what they do back up, Backblaze actually has a special page dedicated to what they don't back up instead. Backblaze offers unlimited storage for your backed up data, and while by default it only backs up files smaller than 4GB, you can bump that up if you need to. Like other online backup services, it runs in the background, backing up your data all the time (or when you schedule it to, if you prefer), and your data is encrypted so only you have access to it. It supports Windows and OS X, and is smart enough to de-dupe data, do incremental backups, and keep backup processes low on system resources. You can read more about Backblaze's features here.
CrashPlan is completely free if you're just doing local backups, but even online backups are affordable, with CrashPlan+ accounts starting at $2/mo (per computer) for 10GB of online backup storage, and going up to $4/mo (per computer) for unlimited online backup storage and $9/mo for unlimited online backup storage for a whole household. You can check out their plans here, and try them free for 30 days with a new account.