Shankhumukham Beach
Located about 8km from the city, this is a popular beach adjacent to the Thiruvananthapuram airport. An indoor recreation club,  Chacha Nehru Traffic Training Park, the Matsya Kanyaka (Nymph) and a restaurant shaped like a star fish are some of the attractions here. Fishermen in boats and the sunset offer spectacular views. During temple festivals the beach witnesses ritual washing of temple idols.

Kovalam Beach
Kovalam located 16kms away from Thiruvananthapuram is one of the majors tourist centers in this part of Kerala. The sandy beaches here are lined with palm-fringed lagoons and rocky coves. Kovalam consists of three adjacent crescent beaches. The southern most, known as the Light house beach, is the most popular of the three. This unique beach could be amongst the loveliest beaches in the world. It is a sheltered bay and is endowed with unusual natural beauty. The beaches are filled with restaurants, most of which serve, delicious sea food. Kovalam is also a centre for Ayurvedic treatment. Many hotels offer complete health and revitalization packages. 
Best season to visit is from December to March. More Details

Varkala Beach  (51km)
Varkala is a very secluded beach situated at a distance of 51km from Thiruvananthapuram, the capital of Kerala. The beach lying on the south west coast of India, is also known as Papnasam beach and is an important Hindu center of pilgrimage. Hundreds of Hindu devotees perform 'Vavubali', a ritual performed for the ancestors soul to rest in peace, on the new moon day of the Malayalam month Karkidam. There is a belief that a dip in the holy waters of this beach will purify your body and soul, washing out all your sins. More Details