Been to the 4 major islands, like Kauai the best, but Maui is alot of fun too. Head down to the southern part of the island. Wailea is where the really nice resorts are, and I think the beaches are better. If you want cheap eats, there is a place called Kihei Cafe that has great cheap breakfasts. Paia is a surfer town to the east of the airport, lots of cool shops, and a great restaurant called Mama's Fish House right on the water. Expensive though. Paia Fish Market has great fish & chips made from Ono, and its cheap. If you are going to do the luau, Do the Old Lahaina Luau. Best one in Hawaii and worth the money.
go buy Maui Revealed. Best guide book out there, and when you do the drive to Hana, they take you to some cool out of the way stuff like a black sand beach that was deserted when my wife and I went.

Blue Pool is also worth the detour. Have fun.