One of the best resort beaches on St. Thomas [1] is at Sapphire Beach, a long beach near Red Hook [2]. Packed white sand provides the backdrop for a perfect day at the shore. A reef runs parallel to the rocky part of the bay; staff at the dive shop on the beach can provide equipment and directions to the best snorkeling. If you prefer to stay on the beach, you will enjoy views of the British Virgin Islands and Pillsbury Sound.
Locals flock to Sapphire Beach on Sunday afternoons when bands play hot soca and calypso tunes. There is also usually a game of beach volleyball going on, too.
Links:
[1] http://www.moon.com/destinations/virgin-islands/st-thomas
[2] http://www.moon.com/destinations/virgin-islands/st-thomas/sights/red-hook-and-the-east-end