"The Encyclopedia of Seashells" is Dr. Gary Rosenberg's treatise on shells. The curator of malacology at the Academy of Natural Sciences of Philadelphia, Rosenberg writes that intertidal mud and sand flats actually have more diverse communities of mollusks than sandy beaches. However, he says there are some beaches where you can find great shells:

In the United States, his pick is Sanibel Island, Florida:

The island's beaches are home to a large variety of shells, including conch and whelk, coquinas and moon snails, says Rosenberg. The shells there are generally in good condition instead of being broken. "It varies from season to season. This past year apparently was very good. People were saying it was like it used to be 30 years ago."

Outside the United States, Rosenberg names Jeffrey's Bay in South Africa:

"Because of the combination of the currents and the wave action, there are often large quantities of shells washed up on the beach. They tend to be more worn than Sanibel because it's a rockier coast."