La Perouse Bay is the name of the spot that I couldn't remember.
http://www.wayfaring.com/maps/show/29
http://www.mauiqueen.com/mauiguide/snorkeling.html
http://www.maui-vacation.net/snorkelmap.html
When I was there I was staying in Kihei and the Kamaole beaches (a series of beaches in town - there are three of them, Kamaole 1, Kamaole 2, Kamaole 3) are even a good spot for snorkeling. Particularly in the morning (6am-8am) before the surf gets really choppy.
There is an element of luck of the draw. If there is an offshore storm, the surf can get enormous, and it makes the water murky. Not a good time to snorkel.
For one you won't see anything, and secondly, the sharks come close in because turtles can't see them coming. Usually this only lasts a few days, and usually there will be another spot elsewhere on the island that isn't affected.
Into windsurfing or up to trying kiteboarding? Some wicked good opportunities on Maui for that.
Sailing, not so much. You'd think you could find a place to rent a Hobie Cat for example. The resorts might but I was really shocked how hard it was to rent a beach cat (well, impossible really, I didn't get to go.
).