Portovenere is one of my favorite places, with a castle (now a contemporary art museum), a Genovese church, cathedral, and many good restaurants serving seafood. The pastel colored houses around the port form a defensive wall around the city, which is entered through an ancient gate.
San Terenzo is associated with the poet Shelly, and is an easy, level walk to Lerici, which has many fine restaurants and a castle as well as a large port for pleasure craft and summer ferries to Tellaro, Portovenere and the Cinque Terre.
Fiascherino, Tellaro, and Montemarcello are traditional fishing villages along the coast. If you have time and a car, take a ride up to Ameglia to see the views of the Magra river framed by the Apuane Alps and the marble mining centers of Massa and Carrara.