My wife and I went out to LA to visit my brother over the Christmas holiday. Everyday was in high 60's to low 70's. It was a wonderful treat for someone from Kansas City.
On Christmas day, we went over to the pier at Huntington Beach. Many people also had the same idea, so it was a great time watching them, the surfers, the beach performers, the volleyball players, and all the other activity that occurs along the pier. You can see a few photos of the pier over at my FLICKR page.
Note that at the very end of the pier is a neat 50's style diner called Ruby's. This is a place well worth the trip. They have good food and service, and a fantastic view of the ocean.