I've noticed a lot of people buying electronic items in St. Maarten. I think the shopping in the islands isn't what it used to be, I'd alsways price things at home first, sometimes there is no real savings.
As for a beach in St. Thomas, a nice beach, but no snorkeling is Meagans Bay. You can even take a cab there and back, plenty there to take the return trip. Its a beautiful calm beach...If you wanted to find a beautiful beach to snorkel, you can take the ferry over to St. Johns, but that involves a good amount of travel time.
I love St. Maarten. If you want jewelry, go to DK International and ask for Deepti. She and her brothers will treat you right, definitely. Also, Last Mango in Paradise (take a right on Front Street when leaving the pier, and go almost all the way to the end, on the right) that has lots of cool Jimmy Buffett-type stuff if you just want some fun souvenirs and t-shirts to take home. Kind of across the street from that is a Delft store, with more blue/white Delftware and pottery than you could ever use. Also, there is a little shop with more costume-type jewelry that I really liked. They have a pretty good selection of Larimar jewelry. I can't remember the name of it and I've been there twice; it's driving me crazy. But I can tell you where it is. You come off the pier, turn right on Front Street, and then take a left onto either the first or second little street or inset you come to, and it's up on the left. It's just a really tiny little shop but cute jewelry. Great for things to take home to family and friends without spending a fortune.
If you don't want to take the ferry to St. John, Megan's Bay is good, but also Coki Beach, next to Coral World. There is some snorkeling there, and lots of beach services.
"When near the sea, one forgets to count the days."
in St. Maarten you have two major shopping choices- downtown on either the Dutch or French sides of the island. You have to take a cab from the pier to get to the French side of the island. You take the water taxi from the pier to ge into downtown on the Dutch side. You can still get decent deals on jewerly, linens, leather goods, liquor, cosmetics and perfumes.
As for the beaches in St. Thomas- Sapphire Beach would be my top pick for a beach with snorkeling on St. Thomas proper. If you want to take the time and make some effort- get over to St. John Island - either on your own, or do the Champagane Catamaran sail (very, very nice) the beaches on St. John are gorgeous - go to www.vinow.com for ferry schedules and beach informations.