When Works pass into the public domain
(University of North Carolina):

http://www.unc.edu/home/unclng/public-d.htm

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Association of American Publishers:

http://www.publishers.org/main/Copyright/copyPermission

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The American Society of Composers,
Authors, and Publishers (ASCAP):

http://www.ascap.com/licensing/about.html

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Sample letter requesting copytright Permission:

http://www.utsystem.edu/OGC/IntellectualProperty/permmm.htm