One reason I like Dropbox. It's a syncing service. All my content are on all my computers. It just so happens I also have a copy of that content on Dropbox's servers (well, technically, Amazon, I guess).
CrashPlan's also pretty interesting, as far as offsite back-ups are concerned.
- Always have your stuff, wherever you are. (+500MB bonus for us both if you sign up via this link)