Molokini was the name of the snorkeling site I couldn't remember when I posted a response to you last month. The best snorkeling off Maui is reached by boat. Molokini is one good spot and the waters surrounding Lanai and off Kaanapali Beach are others.
A friend who has been there recommends several snorkel tour operators, including Trilogy <http://www.sailtrilogy.com> and Navatek <http://www.maui.net/~navatek>. These operators also offer Snuba.