My wife and I got married on Kauai, six years ago this October. By far the best 10 days on vacation. Depending on how much you want to "do" while you're there...
The Na'apali Coast (North) is incredible to hike. All three rivers are great for kayaking and each ends with a waterfall. Secret Beach, ask a local. Poipu is best for body-boarding and surfing. If you like snorkling at all, do not miss Tunnels beach...incredible coral tunnels to snorkle through; be careful though, if the current pulls you out of the tunnels you can become tiger shark bait - they wait below and grab fish exiting the tunnels when the tide is going out (not kidding)! Unless you just like scenic overviews, skip the Waimea canyon (rather boring in comparison to the Grand Canyon). Lastly, look for helicopter tours and, if you're adventurous at all, take the AIR 1 Kauai Rescue tour...no doors, best ride ever!
Have fun, Gig'em, Mahalo!