Here's what I do (with about 3TB data now):
I've got a dedicated backup server at home that backs up all machines there automatically and rsync's the backup to another machine offsite overnight.
I've got an uncapped but relatively slow connection, uplink speed in practice about 2MB/s, but that's enough: it rarely takes more than three hours to do the rsync. Occasionally (like after returning from a two-week trip to Kenya) I've got so much new data (photos) that it takes more than 24 hours, but that's rare (and causes no problems per se, other than increased window of vulnerability, but one day is acceptable for me). Also, both machines have hotswap disk slots, so I could do the sync at home and carry the disks over should I one day get so much new data that rsyncing it over the network would take too long.
This works very well for me. It does require a reasonable network connection and a suitable place for the offsite backup machine, though.