stingray city is awesome you don't even have to get off the boat if you don't want to, you can stay on one of the pontoons and look at all of them, or get in and pet them, they are freaky at first but its fun after that.. shops in town are awesome, and really expensive, there are good restaurants but i think some of the best ones will be where your hotel are. you need to check out Hell too. its a place where rock formations look like flames its pretty cool. they have some of the best snorkeling around though. here is a link to some good snorkeling sites, 7 mile beach is good so is the cemetary and the wreck of geneva. I've been there a few times. if you can you need to check out the first one on there though its awesome, i haven't snorkeled it only dive, but its awesome, called devil's grotto, its gorgeous and deep but if you catch it right you can see all the way down from the top and if you can hold you're breathe for a sec you can check it out pretty good.
http://www.caymanactivityguide.com/Snorkel1.htm