Hi Nick
My hubby and I went in December...I LOVED it!! When are you going? In the winter months, a whale watch is an awesome thing, but they aren't in Maui in the summer, so if you are going soon, you'll miss the whales.
We did a helecopter tour of the island, and it was incredible. I recommend the early bird flight...it departs very early but the mid-day haze can be avoided, and the winds are lower in the early morning. It's a great way to see the island in it's entirety. We flew with Blue Hawaiian Helecopters, and I highly recommend them. They did the flying for the filming of Jurassic Park.
If you plan on a luau, which I also think is a must-do, make it a point to go to the Hyatt Regency. It's called "Drums of the Pacific," and is the only one that features a fire-dancer. The food was easily the best that I have ever had, anywhere, period. The show was also extremely entertaining. It was well worth the cost of the show!
I hear that the sunrise bicycle ride down Haleakala is incredible, but we didn't do that, so maybe someone else can chip in on that.
If you are into history at all, a day trip to Pearl Harbor is a must. I'm not even a history buff, and I found it to be a very touching, sombering experience. While it's a fast trip to Honolulu, and you don't have time to see much, it really brings what happened in 1941 into sharp reality. You can still see and smell the oil leaking from the U.S.S. Arizona on the surface of the water. It's a very emotional experience. We did the Pearl Harbor fly/drive, where we flew over from Maui, got a rental car with the package, and was able to have time to explore the island. Then we went to Pearl Harbor in the afternoon, when the crowds are smaller. It took us about an hour or so to see the film and ride over to the memorial, depending on the crowds.
There are lots of quaint shops up the road in Lahaina. That is where we stayed, and it was a lot of fun.
We did a snorkle to Molokini with the Pacific Whale Foundation, which donates part of it's proceeds to ocean research and preservation, and it was lots of fun. I think if I went back, though, I'd just snorkel on the beach. What was great about that snorkling trip were the many, many dolphins that escorted and played in front of our boat. That was the icing on the cake!! I think I'd do a dolphin-watching trip if I were to do it again, because I enjoyed them so much!
Lastly, the road to Hana is incredible. If you haven't heard of it, do a search online and take a look at what you'll be getting into. If you choose to drive on around the island after you reach Hana, be forewarned: it is pretty scary in places and takes a whole day to drive. If narrow, one-car-wide winding roads and sheer cliffs scare you, it may not be a good idea to go past Hana. I recommend it as a great experience to say that you did, though. If you go on around the island, a four-wheel drive is advised. Don't stop to eat at the hotel in Hana unless you have a fat pocketbook. It is where the rich and famous stay, and we didn't know that when we stopped. We paid close to $50 for a puny, bad salad, a sandwich and two Pepsis.
Above all, take your pocketbook...everything is expensive!!
There is so much to do, and we didn't have time to do it all. Remember to leave yourself some beach time, which we almost didn't do. These were just a few of the great things to do while you are there. Here is a link for some of the different activities that we did, and way to compare prices and companies that provide the services. Be sure to click on the "activities" tab to the left, and not just the "discount activities" on the main page. That way you can see all of them.
http://www.activitysaversmaui.com/
and:
http://www.pacificwhale.org/