Here's a place to start:
The Best Snorkeling in Caribbean | Frommers
I'd add that in addition to the USVI options listed, it's an hour ferry ride to the British Virgin Islands.
The Baths are a famous snorkel destination. DiveBVI runs a snorkel only excursion over to
Anegada since the snorkeling is so good there - it's the 3rd largest barrier reef in the Caribbean. There's also good snorkeling near most of the smaller islands south of Virgin Gorda - need a boat for that. Diving is very good to excellent.
Or Curacao. Easy beach entries and during a week of diving we also found excellent snorkeling. Playa Jeremi gets mentioned in several "best of" lists - there's orange cup corals offshore along the cliffs in water you can stand up in. We also saw turtles in 6' of water off the beach at Varsenbaai and one of the famous dive sites - the Tugboat - is a better snorkel - the boat is 14' deep. At Nos Kas we chased flounder around in the shallows during our SI and at the old Sunset Waters Beach there's a breakwater that makes a natural cove to snorkel in - it doesn't get any deeper than about 6' and must be 100 yds or more across. Just outside of it is a decent dive.
www.curacao.com
Bonaire would have equally good snorkeling in some areas but outside of the resorts, entries there are much more difficult. For diving it's suggested to wear good treaded boots as there's ironshore and coral rubble both on and just off the beach at many of the sites. If you snorkel in full foot fins, that wouldn't work there.
www.infobonaire.com
Bari Reef (most counted species of fish in the Caribbean) would be a good snorkel. There's remnants of an old pier there - found a Batfish hiding in the debris. Windsock Beach is mentioned as a good snorkel site, it's about the easiest shore entry there is on Bonaire. And there's good snorkeling just off Klein Bonaire across the channel. One dive there we moored off the beach and there were turtles hiding in the rocks at the mooring - about 20' or less as I swam in towards the beach filming them. Divers returning from there often see/snorkel with wild dolphins in the channel - we met a group coming back one morning that just had.
It's all very low current there and Aruba (see above) Bonaire and Curacao are below the hurricane belt so generally unaffected. Most days on either island it was flat calm. We were on Bonaire in July and Curacao in May.
I don't know Aruba but Bonaire and Curacao are desert islands so might be too hot for you. I would guess in the sun it was close to 100
o on Bonaire the 1st week of July. The USVI's/BVI's have a constant breeze so it's much cooler - our upscale villa didn't even have A/C.
Last option might be Grand Cayman. The turtle is their national symbol. At Turtle Reef near the Turtle Farm, they frequently get out and live there. It's a little deep to snorkel but an excellent shallow dive. Nearby at Lighthouse Pt. the reef starts in less than 6' of water. Also Cemetery Beach is a better snorkel than dive, Smiths Cove south of Georgetown is another. Google Testudo's Snorkel guide to Grand Cayman for other options. Wall diving there is among the best I've done. The snorkel mentioned in the article is Stingray City - we had a family do that on our dive. Most snorkeling with the rays is done in big groups at Sandbar nearby where you can stand up - IMO it's not as good. Cayman is very expensive also.
hth,
