+1 for Crashplan
Multiple destinations (inc Cloud, USB, network share, friends computer), file versioning, unlimited cloud space, runs silently in the background, mobile device apps to browse archive (if you back up to their servers), pricing seemed reasonable to me.
Carbonite does all of these things as well, but I read that seeding large volumes can take a lot longer as the speed is shaped after a certain amount. This may no longer be the case, but it was at the time I looked into it.