I would recommend the Haleakala bike ride from the Haleakala Bike Company.
www.bikemaui.comInstead of traveling in a tour group, like many of the other shops, you are able to go down at your own pace. Many of the groups I saw had the slowest person in the front. It's cool to be able to go off the main road as well to explore some of the houses, farmland, and other shops.
There is a neat restaurant in Kula, and a good bakery in Makawao called Komoda Store & Bakery.
Would also check out the famous Banzai Pipeline if you are in that area of the island. Not much to see when the ocean is flat though.