Go to Princeville resort have a sunset dinner!!! expensive but great. Or just go for drinks and appetizers.
PostCards in Hanalei,
http://www.postcardscafe.com/
Or to the Beach House in Poipu. Fantasic deserts and dinner right on the beach.
But I LOVE, LOVE< LOVE Tappas at BarAcuda in Hanalei. Dark wood candlelight, great wine and lots of little bites that cost a bundle and are supurb. AND you leave glad you spent every dime! This is where I would go if we could only afford one meal out. We go EVERY time.
http://www.restaurantbaracuda.com/