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.
SpiderOak is well known as one of the most privacy-centric cloud storage services, but it's also a great backup service. The same power and features that you get for file syncing and access extend to its backup client, and SpiderOak's "Zero Knowledge" policy extends to your backups as well. Even they don't know what you're storing on their servers, and all of your data is encrypted on their servers and before it leaves your computer. The SpiderOak desktop client has a fully-featured backup tool in it that lets you back up your entire desktop, documents, email, music, or movies right to the cloud, or you can hit the "Advanced" tab and pick the files and folders you want to save, including external drives, network drives, or anything else on your computer. As you add files to your backup job, you'll get a live preview of how much space you'll use with what kinds of files, and whether you have space for it. SpiderOak supports Windows, OS X, and Linux, has mobile apps for iOS and Android, can do incrementals, and if you uncheck a file to stop backing it up, the files will still live in your SpiderOak account, just as an archive. Your backups happen in the background, or when you schedule them.
Since you're probably going to be paying for a backup service for years, cost is an important factor to consider. All the services rounded up here are subscription-based, but they partition their features and fees differently, so it's worth comparing plans closely before committing to one. Most construct pricing tiers based on the amount of cloud storage included, however, or by the number of devices you can use with an account. A few services offer permanent free accounts, but those plans impose paltry storage limits or restrict key features to the paid versions. Watch out for file-size upload limits as well.
Many services also offer a feature called versioning. This saves incremental changes you make to files as recoverable snapshots of the file. It's useful in case you need to get back information from an earlier version or if your latest file save becomes corrupted. Services vary widely in how many versions they keep and how long they're saved. Best-in-class services, such as SOS Online Backup and SpiderOak ONE keep an unlimited number of file versions forever.
Ben Moore is an Analyst for PCMag's software team covering video streaming services, security software, GNU/Linux, and the occasional PC game. He has previously written for Laptop Mag, Neowin.net, and Tom's Guide. Ben holds a degree in New Media and Digital Design from Fordham University at Lincoln Center, where he served as the Editor-in-Chief of The Observer, the student-run newspaper.