If you like history, politics, or presidential trivia, then I highly suggest the Nixon Library & Museum.
The only negative I would give you is that there is not a lot to do geographically around the library.
The library is currently under reconstruction, so we only saw part of the library. They have a lot of interesting artifacts and pictures from the Nixon years in the White House. They was also an interesting film to watch on the history of Nixon's whole political career. You can also go to the original house that President Nixon lived in as a child, as well as the Presidential helicopter he flew off in after leaving the White House. I would love to go back when the whole reconstruction is finished. It is scheduled to be fully reopen in October 2016.
One thing that is close by is the Angels Stadium. The stadium is old, but it was fun watching the game. If you are a baseball fan then you can go and check it off of your list. Otherwise, I do not think there is anything so spectacular to see.