Definitely bike down Mount Haleakala on Maui. You should sign up with one of the tour groups for the sunrise tour. You have to get up early (like 2 or 3 am), they drive you to the top of the volcano, and you bike downhill 30 miles or so. It was one of the best things we did. We also went horseback riding on one of the other islands which was also great. The road to Hana was fun, but long. You should also go to a Luao (spelling?). Congrats and Enjoy.
Tom