One of the things I've never heard mentioned here is Huntington Library. This wonderful 150 acre ranch in San Marino, CA has some of the greatest old paintings around. The original mansion was turned into an Art Gallery and so were a few other buildings. The original "Blue Boy" and "Pinky" are here. Although we've all seen prints of these paintings for sale everywhere, it was facinating to see the originals. Since I was raised in So. California, I used to try to get out there at least once every summer. I spent long hours going from room to room in the mansion, examining all the paintings.
It is also surrounded by some of the most beautiful botanical gardens in the world. If you are ever in Southern California, this place is really worth a planned day. You can learn more and enjoy some of it through their web site:
http://www.huntington.org/