Do you like to snorkel? We've had several excellent experiences with See and Ski in St. Thomas. For very reasonable rates, we rent a small boat with captain and he takes us to several good snorkel spots. There is always a cooler full of beverages onboard. It's no frills, but for serious snorkelers, it's awesome as you can go where the other people are not, and see exactly what you want to see. We usually bring snacks, but last year our captain took us by the Pizza Pi VI boat and that was an excellent addition to the day!
For Antiqua, Gail at BeachLimerZ is so amazing. You can do a w