There's a huge variety of places to camp it those areas. You have everything from seaside to mountain to desert. What you call camping is open to interpetation too. Do you want to tailgate, backpack, tent, etc?
If you want to tent or car camp you can use Leo Carrillo State park on the beach between Malibu and Ventura. Or you could go up to Chilleo Flats off hwy 2 between La Canada and Wrightwood. Or you could go out to the Devils Punchbowl or Vasquez Rocks.
If you want to hike I'd recommend Mt Pinos (which is always crowded), the PCH trail which runs from Palm Springs North (I really like the stretch between Mt San Antonio and Kratka Ridge), or the Sespe Creek area (Condor Sanctuary).