Three places you haven't been to:
Curacao - starting with the Tugboat, one of the best shore
dives on the east end of the island. It sits in 20' of water. Divers can go deeper around the point while you snorkel. Moving west: at Varsenbaai - while not a great snorkel spot - I did find about 200 squid just off the dive dock and 3-4 turtles feeding on sea grass in 6' of water about 100 yds. east. The owner said they're always there - it was May 2007.
At Habitat Curacao the "beach" has some coral just offshore. I snorkeled there one afternoon - found a barracuda, a bunch of flounder just off the beach and an octopus hole - marked by coral rubble. All in water you could stand up in. The top of the reef there is only about 30' deep a short swim out.
At Playa Jeremi there was good snorkeling all along a rock-face that bordered the cove. The dive was out past it.
There are countless other sites - most with nice beaches also, Porto Marie was one - like you we were diving so oblivious to them. A divebuddy lives in Hitchcock so leaving IAH at 7AM we were on Curacao by about 1:30 - CO thru Miami.
Another option is Maui. Snorkeling is good at: Wailea Beach, Old Airport Beach, Black Rock and probably a dozen other divesites.
Shore Diving Site Listing for: Maui lists divesites that would also be good snorkels.
There wouldn't be a 1/2 dozen Snorkel Bob rental stores if the snorkeling wasn't great there...lol. And you could snorkel off Molokini Crater while others dove. Either with one of the dive operators out of Kihei or one of the big Cats like Pride of Maui or Trilogy - they run combo snorkel/dive trips daily out to Molokini.
Third choice might be the British Virgin Islands - esp. Virgin Gorda. We dove a week with DiveBVI with a snorkeler as part of our group. So we asked them to find dual sites several days of the week. At a couple of them I think he saw more than we did. Several divesites were pinnacles or other rock formations that broke the surface with good snorkeling at the base. - very low current diving also - I don't actually remember any current except at one divesite too deep to snorkel. Around the Indians, Norman, Cooper Islands etc. we often saw snorkelers in the water off private yachts.
Also on Virgin Gorda you've got the famous
Baths - one of the more interesting snorkel sites I've seen - it's too shallow to dive though.
To get to Virgin Gorda, fly to St. Thomas - they have fast ferries that run interisland daily - a five min. cab ride to the port and you can be on Virgin Gorda a couple hrs. later.