The best things to do in Maui would have to be:
1. The road to Hana
2. Scuba diving Molokini (the underwater volcano) and Turtle Town
3. The volcano crater and the drive up
4. Sunrise from the top of the crater
5. Surfing!
Quick Tips:
Most of the discounts can be found in the magazines that are given free around the island, such as coupons for diving trips. My stepfather seemed to be pleased with the windsurfing rentals from Neil Pryde in Kauhului. Also, there's a TimeOut for Maui, and there are lots of local postings in cafes for concerts, which is how we heard about the Steel Pulse raggae concert we went to.
Best Way To Get Around:
Taxi is really nonexistent and pricey unless you're travelling short distances. I would say the best way to get around is by rental car. I think our rental was from Alamo.