We basically snorkeled everyday, the places that we snorkeled included Honolua Bay, Kapalua, and Makena. The snorkeling was fantastic, all the coves listed above provided a whole variety of colorful, amazingly shaped undersea flora and fauna. We also took the Blue Dolphin from Maalea to Molokini and Turtletown. The cruise started very early; on the boat at 6:30am, out of the harbor by 7. The travel was very relaxing and the snorkeling in both locations was outstanding. We saw 3 sea turtles at Turtletown and a variety of fish that were truly exceptional at Molokini.
We also drove to Hana; a 3 hour serpentine drive, through bamboo rain forests, beautiful ocean vistas and literally hundreds of waterfalls. There are a number of local travel books detailing places of interest along the way. These are highly recommended as a way to break the monotony and to be able to periodically inhale some of the local flavor. There is also a tape describing the journey that can be purchased at the Shell gas station in Paia that was recommended to me by friends. The drive to Haleakala is, shorter, higher, very different, but very beautiful, and recommended.
I surfed a number of places on the west shore. Olowaloo, 1000 peaks, Lahaina reef, and the sand bar at Kaanapali. Plenty of places to paddle out with varying crowds. I would recommend a long board because all the locals were riding them.