Snorkeling at Poipu Beach: Excellent close-in snorkeling and a good place for the beginner. Keep an eye peeled for monk seals -- both times we were there, a seal plopped himself down and forced the lifeguards to cordon off part of the beach.

Kilauea Lighthouse: Spectacular views, great bird-watching, and friendly and knowledgeable volunteers to answer your questions. Don't be cheap, make sure you pay the $3 honor system fee at the entrance. It's worth it!

Waimea Canyon: One of the most spectacular places on earth. Stop at all the different lookouts -- each offers it's own perspective. And if the canyon isn't awesome enough, the views of the Na Pali coast from the Kalalau Lookout and the Pu'u O Kila Lookout are unbelievable! It's frequently fogged in, so the earlier you get there the better. See my overview for pictures.

Wailua Falls, Opaeka'a Falls, Hawaiian Village: The viewpoints of the these falls are quite nice although they just make you wish there was a way to get closer to them (there probably is, but it ain't easy!). Just past Opaeka'a Falls is a steep road down to the Wailua River and the Kamikomoa (I think) historic Hawaiian village which gets very little mention in the guidebooks. For $5, you can take a self-guided tour of the grounds which are quite interesting with many restored authentic buildings. Some movie scenes from Outbreak were filmed here. The folks there were very nice and also offer kayak rentals ($25 adults/$15 kids for all day). Because they are further up river than the other kayak places, you can get to the Fern Grotto and Secret Falls that much quicker.