The helicopter ride is expensive, but it's worth it. Here's a link the the company that I used, and I think they're the only ones that will take you up with the door removed.
http://www.interislandhelicopters.com/
Other than that, I'd suggest hiking at least part of the NaPali coast, but you can't really go wrong with anything on the island. If you take a snorkling tour, make sure that snorkling is guaranteed, because we spent the day on a boat only to be told that the water was too cloudy and that there could be sharks.
Anyway, it's the most beautiful and relaxing place I've been, and you should have a great time as long as you aren't looking for nightlife because there isn't a whole lot of that.