I agree the Road to Hana is long but if you like to hike there is an awesome trail at the end called the Pipiwai trail. You hike thru a bamboo forest and see a nice waterfall but the payoff is at the end (2 miles or so) where there is a huge waterfall that you can stand under. It is very nice!
Also, if you go north past Kapulua and don't get freaked out by scary drives (much scarier than Hana) you can see beautiful scenery and stop and get some great banana bread at a roadside stand.
Another must do is snorkeling. You can rent gear and go on your own or do a boat tour. I like being on a boat so we did that and we got to see lots of turtles and dolphins.
Boogie boarding in the Ocean is fun too and just relaxing on the beach.
We did the Luau at "The Feast of Lele", I think they are overrated but the women love them. This is probably a must do if it is your first time.
Check out the book "Maui Revealed" for lots of info on where to stay, eat, see. It is a great book but some people think they have gone too far.
Maui is one of my favorite places in the world and hope to go again soon!