For a private tour guide who delivers a cultural connection to the island, Pono of Open Eye Private Tours (808/572-3483, www.openeyetours.com) has been a private tour guide on Maui since 1983, and communicates with the clients before the tour to get an assessment of of what sort of activities might suit them best.
For visitors who have an interest in music or dance he might arrange a tour where hula dancers from a local halau offer a private performance with chants which relate to the land around you. If you're interested in the spirituality of the islands, Pono can arrange an itinerary of places which are steeped in Hawaiian mythology and spirit. As a former teacher, Pono also specializes in tours with children and offers activities for kids such as making fish out of coconut leaves.
In the end, what make Pono's services so unique is that you get to visit places where few other people get to go. It's not because he tramples over private land, but because he's built up contacts over 30 years which enable him to bring guests to the properties of local people who regard him as a friend. A large tour bus of 45 people won't be able to stop at a taro field on the way to Hana and pull taro with the owners, but a private tour with Pono will provide you with experiences which simply aren't available to those traveling with a big group (or on their own for that matter). Since the tours are private they're much pricier than other options, but after a day spent with Pono you won't be disappointed. He'll even write you a Christmas card.