The southern Peruvian Pacific coast is mostly desert. If you just want to lay on a beach, stay to the north. For archaeological travel on the coast, sand boarding on sand dunes and close access to some of the highlights in the Andes, your best bet is the south. Some highlights on the southern Peruvian coast include:
Nazca: A small town in the middle of the desert, Nazca's biggest attraction is the Nazca Lines — mysterious lines and figures etched into the landscape on the desert coast of Peru. They are now a World Heritage Site and are best seen from the air. There is more to Nazca, however, such as adventure travel, some very nice hotels and a number of parks.
Ica, population 152,000, is in the middle of dune-filled deserts on the banks of the Ica River and offers nearby sand boarding (like snowboarding but on the sand dunes) as well as tours of local graperies, wineries and distilleries.