Peter Hirtle. Copyright and Cultural Institutions: Guidelines for digitization for U.S. libraries, archives and museums, Cornell University Press, 2009.
Stanford University, Copyright and fair use. http://fairuse.stanford.edu. The fair use section is particularly good.
Richard Stim, Dear Rich: an intellectual property blog, http://dearrichblog.blogspot.com. Written by an attorney but geared toward the non-lawyer.
U.S Copyright Office, http://www.copyright.gov. Includes information on copyright registration, educational circulars, and information on current issues.