PSA: with CrashPlan, you can simultaneously backup to your own server(s) or external hard drives right alongside their service. You can also backup to a friend's computer (this was actually their original business model--P2P backup).

Clarification: you can back up to your own servers iff said servers are also running Crashplan. What you can't do, unfortunately, is back up to an ordinary shared folder.

Further clarification: this is correct, but (if someone is reading this and thinking about doing it), you can install the free version of CrashPlan and it works just fine as a backup server.

It's kind of a ram hog, though.