We used this company for the ziplining and it was awesome!!!
I planned a two week vacation to Hawaii- one week in Kauai and one in Maui and used the tripadvisor forums, but honestly had better input/planning from the Revealed books. Kauai: Revealed was a lifesaver for us.
We went ziplining with Kauai Backcountry and took a helicopter tour with Jack Harter:
http://www.helicopters-kauai.com/index.html. We also did some stuff on our own like the NaPali hike to Hanakapi'ai beach on the Kalalau trail (one of our favorites). We did a boat tour with Captain Andy's as well:
http://www.napali.com/tours/ (we did the snorkel BBQ one). You can't see the Napali coast except by helicopter, boat and hiking (so I guess we did all three!). We usually did an activity in the morning then hung by the pool/beach in the afternoon. We stayed at the Kauai Marriott and it was absolutely amazing- best pool ever. We used the book for a lot of off the beaten path locals restaurants and even picked up some food at Costco (along with $1.50 hot dogs for lunch).