The beach at Redondo is probably at the top of the list for free activities.  There are annual events held there such as the International Surf Festival or the Kite Fesitival that are extremely popular with the locals.  Another favorite is the local boat parade held on a Saturday in December each year.  Even if there isn't anything scheduled, it's nice to walk around the Redondo Beach pier and experience the atmosphere.  If you travel a few minutes southwest, you can drive around the Palos Verdes peninsula.  If you decide to do that, be sure to take the Paseo Del Mar route along the edge of the peninsula.