Jonathan has three iMacs and he's looking for a backup solution for all of them. He uses SuperDuper for one. Leo says that one choice is an external hard drive for each, but that wouldn't do off site backup. That's why Leo recommends using a centralized Network Attached Storage (NAS) and backup to that. Synology is a good option. It uses Disc Station software that will automatically do the backups and then backup to the cloud like Carbonite with a plugin. Drobo is another one.
(Disclaimer: Carbonite and Drobo are sponsors)