Head to Kanaha Beach Park on Maui's windward coast to see some of the world's best adrenaline-juice junkies go kiteboarding, zipping airborne on a sail with a surfboard clipped to their feet. The trick for the boarders (among many tricks, including having the cohones to do it) is to have the right amount of sail for their body weight so that they can swing above big waves in a pendulum motion, and not go lifting off into the Pacific skies. These guys and wahines come from around the world.
Windsurfers also like Kanaha, as much almost as they do the glamor-puss spot for this sport, Hookipa, which is a few miles down the coast. You won't believe how close it is to the airport, though it's not on main roads. See the Maui Trailblazer guidebook for more.