i can tell you about a few spots i really like in the general Los Angeles area. for hiking that is.
most of my camping experiences are in NorCal.
great hikes around LA:
1) Temescal Canyon (Pacific Pallisades)- there is a loop trail that goes past a waterfall (rarely flowing) up to a ridge with a great view of the ocean past Pacific Pallisades. about a 2 hour hike - moderate
2) Ed Davis / Towsley Canyon (Santa Clarita) - another great loop trail that goes through some amazing rock formations up the ridge with great views and back down. there are some tar pits along the way. about 2.5-3 hours - moderate difficulty.
3) Griffith Park - there are a ton of trails in there. i like to start at Ferndell Picnic area and go past the Observatory to the top of Mt. Lee. great 360 view of large parts of LA. - about 2 hours - easy/moderate.
4) Eagle Rock (Topenga Canyon) - neat big rock with great views. tough on hot days as there is very little shade anywhere. 3 hours - moderate.
hope that was any help at all.
good luck man. enjoy the trails.