Hi Kristin615, welcome to Cruise-Chat. Not sure if you're going to Dominica or not, but if you are, do the Champagne Reef snorkel-awesome! Trunk Bay that Casey and Kathy mentioned is beautiful and there's a great snorkel about 50 yards off shore. Sapphire Beach is ok, lots of small rocks when you're trying to get into the water. If the wind isn't blowing too hard, the snorkeling is ok. If you're going to Grenada, Flamingo Bay is a fantastic snorkel. If Tortolla is one of your ports, there are some good snorkels at Norman's Island. If St. Lucia is one of your ports, the Piton snorkel is good. If Barbados is one of your ports, the Tiami Catamaran sail/snorkel is really good.
Hope this helps some. Have a fantastic cruise, and once again, welcome aboard!