Mondello is Palermo's main beach, a wide arc of white sand just 8km west of the city centre. You can reach it by bus or car, and in summer it is packed with locals. The setting is lovely, hemmed in by Monte Pellegrino and the headland of Capo Gallo. Chairs and umbrellas are available for rent, or you can find free stretches if you walk a bit.
Arenella is a smaller, less crowded alternative in the Addaura area. For something more remote, Pollina beach lies about 85km east along the coast and offers clean water and rocky scenery without the crowds.