Reading about everyone's drive-in movie theater experiences has made me feel nostalgic as well, so I searched the Web and found two great sites:
http://www.driveinmovie.com/CA.htm lists California locations and brief historical info about past and current drive-in movie theaters.
http://www.driveinmovie.com/mainmenu.htm is the main site that lists information for drive-in movie theaters across the United States.