I use spider oak for this. I believe there is a opensource non-hosted alternative.
Google for open source alternatives to spider-oak one. SO1 has encryption, and its only client side placed,
hosting co. doesn't even have key.
This violates your "google results" stipulations, but this is a good email topic to intro people to SO1 and
SO1 alternatives, and you may find exactly what you want. For now I am fine with hosted solution, as its also offsite.
But eventually wouldn't mind non-hosted, and started to look for that, and there were some claims that there is stuff out there.
-tl