Bring an oxygen tank if you can; try not to breathe the air there.
Seriously though... Check out the John Paul Getty museum. It's pretty cool. The artwork isn't all that fabulous, but the building and grounds are a work of art, and provide some of the best views of L.A.
We took a guided tour of the city on through a company called "VIP Tours". That showed us a little bit of everything in L.A. (Venice Beach, Beverly Hills, Downtown, Hollywood, etc.) and we went back to the things that we liked.
Be sure to rent a car, because public transportation does not exist.