Anywhere you can walk into calm water to snorkel is a good spot.
I really like snorkeling the rocks on either side of Devil's Bay at the baths. You can walk in right off the beach.

If you make it to Trunk Bay, St. John, USVI there's a nice beginner snorkel off the beach that follows concrete guides on the bottom.

There are easy snorkels off the beach around The Big Bamboo, north shore Anegada. Just don't go out too far.