Swimmimg with the rays is cool. Make sure you get to feed them. Snorkeling/diving is incredible there.
There is a cool bar with steps that lead into the water. I cant recall the bars name, but the attached restaraunt is the Cracked Conch.
The Ritz is amazing. Enjoy the floating beds in the water, while watching sunsets, or just checking out the moon, while sipping a rum drink.
It is very expensive there, but if you are careful, you can stretch your money out a bit.
Walking along seven mile beach ( really only like 5) is pretty amazing. The sand is so soft and white. We walked up the beach for a couple miles one day and found some taco shack next to the beach. Great fish tacos. I dont recall the name of the place though, sorry.