Location: several on the island
Features: takes you around the island
Although it's not really one of my favorites to take guided tours, I think a helicopter flight on Kauai is a must for every visitor, especially if you come from europe and only have one week on Kauai. There are simply places you can only see by helicopter. I also shoot my best pictures on that one-hour-trip.
There are probably over a dozen companies, offering airtrips like that, so the choice is yours. We took one of the 'cheaper' categories, but even that one was fantastic. It was an one-hour trip for about 140$. They also offer shorter trips, but from my point of view, that's not worth the money.
A good starting point is Hanapepe at the south coast, because you're right at the attractions and don't have to spend your money on the flight TO them. Best time is probably early in the morning, because the air is clear and later the day, the mountains are usually in the clouds then. The one-hour trip basically takes you to the major attractions like Waimea Canyon, Na Pali Coast, Hanalei Valley, Mt. Wai'ale'ale and so on...check out some impressions below.
Hanalai Valley / Nu'alolo Cliff Trail / Na Pali Coast / Salt Pond Beach Park, Helicopter Flight / Waimea Canyon / Wailua Falls