The snorkeling off of Black Rock is superb. We saw turtles, eels, tangs, idols and a small shark. Black Rock is in front of the Sheraton right on Kaanapali beach. I loved being able to walk right off the beach and start snorkeling without having to take a boat and spending money. For a day trip, take a trip out to Molokini. Molokini is a sunken volcano crater that makes a sort of lagoon. Most tours after going to Molokini take you to a second spot for turtles, dolphins, ect. For Black Rock or Molokini, morning trips are preferred. After about lunchtime, the winds pick up affecting visibility. Other good places are supposed to be Kapalua and Napili - but I don't have any first hand knowledge of them. I was there in 2004 and am going to Oahu this summer.