Maui
Ed Robinson - One of two "most recommended" operations on Maui (based on my non-scientific observations). I have been diving with them a couple of times and have generally had good experiences. Leaves from Kihei.
Mike Severns - I have not been out with Mike Severns but generally those who have recommend the operation highly. Leaves from Kihei.
B & B Scuba - Seems to be more of a local oriented shop. I really enjoyed the two days of diving I had with them a couple of years ago. I definitely would try them. They also leave from Kihei but a touch earlier to beat the crowds at Molokini.
Lahaina Divers - Some people describe Lahaina Divers as a "cattle boat" operation. I have generally had pretty good experiences with them and if you are staying near Lahaina, it is a much shorter drive to go out with them. Another plus is that they are closer to the "Cathedrals" which is a great dive.
Reeflections - This operator is a great photographer who will take you on your own guided dive. Want to work on your photography skills. This is the place.
Kayak Diving in Maui - Learn a little about kayak diving on Maui.
Aloha Bike Tours - Want to ride a bike down Haleakala without wearing a motorcycle helmet and actually peddling once in a while. This is your operation. Run by a real bike rider.
Haleakala - You have to see the sunrise here.
Ulalena - Great show. Worth the $$ in my opinion.
Maui Ocean Center - Aquarium - Even divers will enjoy this.
Pacific Whale Foundation - I recommend the Pacific Whale Foundation if you are there to go whale watching.