I would have written exactly what diversteve did. Debbie and I have been diving Hawaii once a year since 1998, mostly on Maui, though also Kona. I actually certified through Maui Dive Shop back when they ran excursions from Kihei, Lahaina and elsewhere. Now, although the have several retail outlets, they operate only from Maalea. They are "everywhere" though for tank and weight rentals, and they will rent you a dive flag if you don't have one. They will rent all gear you may need. We stay near Lahaina, and have grown to be very comfortable with Lahaina divers, who depart right from Lahaina harbor, and go everywhere from there: Molokini, Lanai, Molokai for hammerheads, and many local sites that are great: The Carpathian, Olawalu, Mal pier, and scores of others. I think the best sites are on the West side of Maui, and from there Lanai is a shorter boat ride that from other places, though the run down to Molokini is a little longer. Have a great trip!
DivemasterDennis