The Mar del Plata in Argentina is perhaps one of the best beach resorts in the country. It is packed with people swimming, watching street performers on the Plaza Colon, and walking the port. The best time to visit this place is in Spring and Autumn, when the area is not so crowded.
The Pier House Resort & Spa in Key West sits on the edge of Key West's Old Town. The 142-room hotel has a private beach and strikes a lovely balance between sandy bliss and traditional Key West quirkiness.