Grand Cayman: Sting Ray Sandbar (many call it Sting Ray City, but Sting Ray City is for divers, Sting Ray Sandbar is for standing waist deep in water)
Ocho Rios: You have to do Dunns Falls. Its a blast. Go on www.google.com
(or search these forums) and look up Peat Taylor. He'll give you a full day of touring, including Dunns Falls, for $30/person. Its a real bargain and I'm sure you'll have a good time (and a safe one).