Observatory is free. Parking can be rough and you may be hoofing it for some distance. Griffith park also has a lot to offer, including a carousel and the old LA Zoo where you can walk into the cages where they use to keep the animals. Hollywood sign is next to Griffith park as well.
Great theme park with rides, shows, studio tour, and Harry Potter land. A free option is to visit the Universal City Walk which is mainly a mall like outdoor strip, before the entrance to the park (Picture on this is from City Walk)
Not the original zoo. Separate zoo north of San Diego.