A delightful finish to the Marin Headlands loop, Rodeo Beach is a popular and accessible beach just a short drive from the Golden Gate Bridge (the fast and furious can hike there from the bridge).
Great hiking, mountain biking and birdwatching complement the usual beach pleasures (including surfing).
Website: http://www.parksconservancy.org/visit/park.asp?park=74
Wikipedia: http://en.wikipedia.org/wiki/Rodeo_Beach