We had stayed, back in July of 2008, at the Bass Harbor campground in Bass Harbor, Maine. It was just outside of Acadia National Park and only about 1/2 mile from the ocean. I would bike down to the lighthouse to get pictures in the morning and evening and it was very beautiful.
The downside of this park was that it was quite far from the park since the inlets don't allow a direct route. There is (or at least was
) a shuttle bus that we took most of the time to get to the park. It saved me from having to drive everywhere but it added time. The park, at the time, was being slowely renovated and we would stay there again. I enjoyed that it was away from the hustle and bustle, very relaxing. I do recall that the sites were pretty close together but that didn't bother us since we were rarely there.
Acadia has wonderful bike paths but you need to know that there is very little of it that is level so it will be a workout but I considered it to be well worth it.