Services such as CrashPlan, Backblaze and Livedrive let you send your files to their servers over the Internet, for a fee. If you do this, then your Mac and any local backups you have on the premises next to it can be stolen, smashed, burned or drowned, but there’s a copy of your data held in a remote location, in a facility that is usually itself secure and which has good data redundancy.
Don’t confuse this with services such as Dropbox, which, while they do broadly the same thing at a technical level, are only designed for tiny subsets of your data, not the whole lot—and it’d be just your luck if you haven’t put the thing you want in the safe directory to be backed up.
Good because: All your data gets sent away to a secure location, so is protected from theft and local disasters. Happens all the time you have an internet connection (so great if you travel on business), rather than requiring you to be on your home network as with a Time Capsule, say. Sometimes some versioning.
But be aware that: Takes a long time to complete the initial backup on most broadband connections, and could take an impractically long time to restore a full system back again. Unlikely to be an option on a capped or slow connection. Cost can mount up—though do explore “family” plans if you want to get everyone backing up.
Aside: iCloud’s backup abilities
iCloud can back up key information—addresses, bookmarks, and keychain items, for example—and also back up your photo library and any documents stored on iCloud Drive. Just be careful: it’s easy to misconfigure things and to discover too late that you haven’t backed up the things you thought you had. Pay close attention to the iCloud pane of System Preferences; don’t just think “I have iCloud” because it doesn’t work the same on the Mac as the backup system does on iOS.