There are many types of reference sources, including dictionaries, encyclopedias, biographical dictionaries, atlases, and chronologies. They provide background information on a topic and can quickly prepare you for more in-depth research. They can also lead you to other sources if you read closely and make note of works cited that you might be interested in.
The Film Encyclopedia by 
International Dictionary of Films and Filmmakers by 
Encyclopedia of Filmmakers by 
The New Biographical Dictionary of Film by 