Bear is pretty sick.. when they have pow and open the canyons there is some insane tree skiing in there. lots of fun. They also have a sick park...
Snow summit is sick as well, just next door, and they put out a sick park every year...
Mt. High is another big park resort. Not much for steeps, but they are the closest, and they put out a pretty cool park with very unique features.
Mt. Baldy is by far the best for pow and such, but they havent had anything much over the last two years I think... especially last year. Horrible year for Baldy. When they get a few big dumps, they are by far one of the sickest and steepest places in the state (tahoe and Mammoth included) if not Socal...
Those are the big 4 in Socal...
Up the road though, is mammoth.. which is always sick and I need not explain, and June is fantastic to ditch the crowds on busys. They have some pretty sweet steep runs and a ussually huge park.