I use CrashPlan www.crashplan.com
, which has very good reviews and it has different pricing options according to your needs.
Just in case, I haven't required to do any restore so far.
I would advise against eliminating one of your physical drives. Online backups offer an additional recovery possibility for your files, especially in cases of disaster or media loss, but the speed of backup or recovery depends on your internet connection and it could take very long to restore image libraries, where sizes in the hundred of GB or even TB are common.