Malibu's Point Dume Beach has got to be my favorite all time beach. Its a great place to get away from the city and leave your troubles behind. The beach mostly is a private, but you will definitely find beautiful seals and surfers.
Salton Sea is not technically LA, but is a by-product of its history and my first-choice escape from the city: one of the world's largest inland seas and lowest spots on earth, a man-made lake in the midst of the Colorado desert, a resort area in the twenties turned in one of the worst ecological disaster of the past century.
It's a cemetery, but the view from up here is stunning and you can see one of the most large scale epic paintings ever made by a human: The Crucifixion painting, by Polish artist Jan Styka. It's a must see.