U.S. Copyright Office - Copyright Information Circulars and Factsheets:
Copyright Basics (Circular 1)
http://www.copyright.gov/circs/circ1.html
Duration of Copyright: Provisions of the Law Dealing with the Length of Copyright Protection (Circular 15a)
http://www.copyright.gov/circs/circ15t.html
How to Investigate the Copyright Status of a Work (Circular 22)
http://www.loc.gov/copyright/circs/circ22.html
The above links are only three of the very useful primers available through a site maintained by the Library of Congress in conjunction with the U.S. Copyright Office. Most of these documents are also available for download in PDF format. The full list of Circulars and Factsheets is available at http://lcweb.loc.gov/copyright/circs/
When Works Pass Into The Public Domain
A simple chart explaining the relevant U.S. Copyright law in relation to the age of a work. Created and updated by Laura N. Gasaway, Director of the Law Library & Professor of Law, University of North Carolina. Incidentally, this is one of the most linked to web pages on the Internet for Copyright information.
http://www.unc.edu/%7Eunclng/public-d.htm
NELINET Digital Library Resources on Copyright
A very good collection of sites with brief annotations on linked sites, page also includes links to sites on Digital Watermarks. NELINET is a non-profit membership cooperative of libraries on New England.
http://www.nelinet.net/necol/resources.htm
Copyright Resources on the Internet
An extraordinary collection of links to information on all aspects of U.S. Copyright law. This site is part of a Copyright Implementation Manual for Teachers, Library Media Specialists and School Administrators of the Groton (Connecticut) Public Schools.
http://groton.k12.ct.us/mts/pt2a.htm
10 Big Myths about copyright explained
After you feel fairly comfortable with copyright lingo, here's an entertaining essay on ten misconceptions.
http://www.templetons.com/brad/copymyths.html
