The ideal solution is the Quadfecta (is that a word?) - Dropbox for (in my experience) excellent versioning/synchronizing (Never failed me) + Backblaze (or its ilk) for continuous Offline backups + Super Duper (weekly/whenever) - for Image Backups - + Something (Arq?) on top of Glacier for long time off-site-archival.

For $50 in software (Arq+SuperDuper), $100 for an external HD, and less than $25/month ($4-backblaze, $10 Dropbox, $10 Glacier) you have a backup system that is next to air tight for a Terabyte of Data and a working set (on dropbox) of 100 Gigabytes.