The Copyright Information Center from Cornell University has good information on Copyright Basics and a Fair Use Checklist.
Copyright and Fair Use FAQ from Stanford University's Copyright and Fair Use Center includes extensive information on copyright law, including fair use, the public domain, and academic & educational permissions.
The video below, from the Copyright Clearance Center gives a basic overview of concepts related to copyright law.
The Center for Media and Social Impact has created a series of videos demonstrating fair use and documentaries:
The video below, an example clip (0:38s) from Michael Kirk's PBS documentary "Karl Rove- The Architect" demonstrates the filmmaker taking advantage of fair use to include a 1973 CBS news clip in his documentary in order to make the point that his subject, Karl Rove, has had a long-standing interest in electoral strategies.
Take a look at the many more clips from professional documentaries demonstrating filmmakers taking advantage of fair use on the Center's YouTube channel.
Creative Commons works can be useful sources for documentarians. What is Creative Commons? This video explains.
Email: refdesk@millikin.edu