Hi peggyellis, welcome to Cruise-Chat! If you'll look a little further down on our main page, there is a Caribbean Port Chat section. Using your "Find" feature in the upper left hand corner, you can type in your ports and it will pull up all the posts made about them.
Cruise Fanatic is spot on, Trunk Bay on St. Johns it awesome! The water is crystal clear, there's a self-guided snorkel trail about 50 yards from the beach, and all the ammenities you need. However, if traveling to St. Johns is not for you, there are some beautiful beaches in St. Thomas. Coki Beach is much like Magen's Bay, in that you have all the ammenities. Sapphire Beach is great for snorkeling if the wind isn't blowing too much, but is sparse with ammenities. It has a store to purchase something to drink and it does have restrooms and places to rent beach equipment, but not as abundant as Coki or Magens. Still, if you like snorkeling, it's a good place. The water is beautiful, too.
They do have facilities, IslandCruz. It's much better than Sapphire. There is a bar/restaurant area, chair/umbrella rental, snorkeling gear rentals, restrooms, and I believe there were lockers there, too. There's some shaded areas available. If you have a nice driver, he can stop at a couple of turn-outs for some great picture taking. One of these times, I want to try out Pineapple Beach. The crew on the Emerald Princess was telling me that that's where they went. I don't know what facilities it has, if any, but wanted to check it out.