If you're into seeing some side-show types, Venice Beach is your best bet.
For a nude beach, there is San Onofre State Beach but it's a good hour south of LA. The problem here is there's mostly young gay fellas hanging out there (no pun intended).
If you want a girl-watching beach, nothing beats Huntington State Beach and Bolsa Chica State Beach. Even David Hasselhoff concedes that the best babes show up out there. Expect a good 1/2 hour drive south from LA. I've spent a lot of time out there and I've got to say, it's an uplifting experience!
For beach-side camping, check out McGrath State Beach in Ventura or Doheny State Beach in Dana Point. Doheny has some pretty good surf also.
Does that cover all the bases?