[scottmandue]

Obviously Richard nailed it...
Limahuli Valley botanical gardens was very nice, if you are not big into plants the docents will regale you with a lot local history and legend on the tour.
A little further up the road form the botanical garden is the end of the road, Ke'e beach (great snorkleing!!!!) and the start of the Na Pali trail (beware of slipery/mossy rocks if it is raining)
Highly recommend a helicopter tour... so much of the island is lush and inaccessible you get to see a lot of undisturbed beauty.
For lounging on the beach and body surfing Hanalei bay is hard to beat (my family usually rents a house there)

The Na Pali boat tour is very cool too, done that a couple times, smooth seas=great, high swell=you will come home with a black and blue butt.
Enjoy!