Honeymoon Beach
Honeymoon Beach is actually connected to Salomon Bay. They are separated by a rocky reef that offers very good snorkeling possibilities.
Like Salomon Bay, Honeymoon Beach is quiet and secluded. It can only be reached by a 1 mile hike or via boat. While the snorkeling is good enough to warrant some tour traffic, the beach rarely attracts enough people to be considered 'busy'. This isn't for lack of beauty - Honeymoon Beach is beautiful and offers everything any other St. John beach would. This only covers the natural side of things of course, as there are no vendors or other amenities available at the beach.
Honeymoon beach is a great spot if you're looking for a quiet day away from most everyone. You won't be fighting for a prime spot on the sand.