Here are my suggestions:
1. St. Thomas-If you want to stay on the island, Coki Beach or Megan's Bay are nice beaches. Sapphire is a good beach for snorkeling, but not a whole lot of ammenities there. If you don't mind a little venturing, grab a cab to Red Hook and take the ferry over to St. John. Then grab a cab to Trunk Bay. We've also done some great catamaran sail/snorkels out of St. Thomas.
2. Dominica-Champagne Reef snorkeling. I prefer going in a catamaran, but it can be done from the shore. One of the best snorkels I've ever had. Trafalga Falls and the Emerald Pool are also nice.
3. Barbados-Tiami Catamaran sail/snorkel, great excursion. Good snorkel, nice beach, great crew, beautifully kept catamaran. If you like spicy food, try the bajan pepper sauce.
4. St. Lucia-Pigeon Island or a snorkel to the pitons.
5. Antigua-we covered.
6. St. Kitts-there's a fort there with a beautiful view, and we also visited a batik factory there. The snorkeling is not that great there. It's not bad, but just not as good as the other islands. I think JimC went to a beach there.
If you'd like to find all the posts made about these ports, use the "find" feature in the upper left hand corner. Type in your ports and it will pull up all the posts made about them. Maybe there will be something that really sparks interest.