Kauai is almost akin to a theme park in that you can see some of the most different and spectacular scenery in such a short time, and the best way to see it is by helicopter. From the almost arid beauty of Waimeia Canyon to the lush vegetation just below the cloud covered summit of Mount Wai ele ele (one of the wettest places on Earth), 45 minutes in the air will make you feel like you've been jetting from one continent to another. Okay, that's an exaggeration, but you will see natural beauty that truly leaves you in awe. It's pricey, although you can sometimes reduce the cost by attending a timeshare presentation (hey, that's what lured me to the island in the first place), but it's worth every penny, whether you do it once or every time you visit the island.
Most of the helicopter services take great pains to enhance the visibility for all passengers. Some offer a videotape (with your own narration) of each trip. There are packages of all kinds, from straight flyovers of the island to multi-hour trips that feature a landing and meal by a remote waterfall. Enjoy!