I know some people that use Ultra Home Internet on the islands of Winnipesaukee. They are reasonably priced if you do not need a large amount of data per month. If you need unlimited data they are a bit pricy.
I did some testing this summer on Bear Island and found the performance to be good enough for basic web browsing, email, etc. Streaming video worked but chewed in your data allowance quickly.
Read my full
Ultra Home Internet Review