Kauai is probably my most favorite place on this earth. It is so peaceful; its almost like a secret from the rest of the world that is in such plain view.
With Princeville, Poipu Bay, and the Kauai Lagoons courses, it is a decent place to golf as well. And I can tell you from experience that the Mariott on Kauai is the most stunning, accommodating, beautiful, fun, and hospitable hotels I have EVER stayed in.
Maui is also a great destination, with Kapalua and Kaanapali real close (Though I think Kaanapali kind of lacks.) If you make your way over to Haleakala, try to play Pukalani... its a great little public course that probably has the most elevation changes on any one golf course I have ever played, as it is built half way up on the slopes of the 10000 foot volcano.
Oahu I haven't had much golf experience on, but there is Ko'Olina, Ko'Olau (the "most difficult" golf course in the world) among many others in the Honolulu area. The Marriott there is very nice as well, and RIGHT on Waikiki beach, though I think Honolulu takes away from what Hawaii is meant to be as a vacation spot, as it is the state's capital and there are actually businesses there.
As for the Big Island, I can't tell you very much. My brother or Dad could tell you far more than I as they have both played there many, many times, and there are some great courses down there.
If you can make it, try to make a day trip to Lanai'i as I have heard the 2 courses there (The Challenge and The Experience) make a great Hawaiian golf 36-Hole Day, and the Island is only 1 city, so it is very tiny and makes for a great day trip.
Enjoy!!!!