Popular Maho Beach has one of the most unusual locations you will ever see. When planes land on St. Maarten they fly right over it. This is the closest observation point in the world where the public can watch planes as large as 747's land.
The beach is surprisingly good, and the snorkeling is great. The surf can sometimes be rough but it is a great place to stop, take a quick dip and watch a few jets land right over head.
A Word of Caution - Regardless of what other people do, stand off to the side of the runway. The jet blast could toss a pebble back at you at twice the speed of a magnum bullet. Also don't leave your clothes or towels in the flight path or they will be blown out to sea.
At one end is the Sunset Beach Bar
a very popular and always crowded spot on the other end is the Driftwood Beach Bar
where you get a bit more individual service and some very delicious cocktails.