One of the best ways to see any of the Hawaiian Islands is by helicopter. From the air you'll see many things that can't be seen at all from the ground. You'll also see more of an island than you can in many days traveling in a car.
I often encourage visitors to schedule a helicopter tour early in their vacation. I do this for two reasons. First, it gives you a great overview of an island and helps you decide where you'd like to explore in more detail from the ground. Secondly, and just as important, if bad weather sets in, you'll still have time to reschedule your flight for later in your trip.
When I was on Oahu in March, I had the chance to take a circle island tour with Makani Kai Helicopters. They fly out of the Honolulu International Airport and the Ko Olina Resort in Leeward Oahu. It was a great experience to see such places as Pearl Harbor, Waikiki and the North Shore from the air.