-We loved the Mel Fisher Museum (http://www.melfisher.org/). Great shipwreck/treasure stuff.
-Best meal we had was at Latitudes on Sunset Key (http://www.westinsunsetkeycottages.com/latitudes-restaurant)--great setting on a little island just across from Mallory Square.
-Hit sunset at the pier once at least. Try to catch the guy with the trained cats. It's a hoot.