BMIBroadcast Music, Inc. collects license fees from businesses that use music, which it distributes as royalties to songwriters, composers & music publishers. This is one of a couple of sites you can search to see if something is still under copyright.
Copyright.gov: U.S. Copyright Office: Search Copyright InformationWorks registered and documents recorded by the U.S. Copyright Office since January 1, 1978. Allows users to (1)search records of registered books, music, art, and periodicals, and other works. Includes copyright ownership documents and (2) find records prior to 1/1/1978 and also register a copyright, record a document, and get copies of Copyright Office records. Check out the "Fair Use Index!"
Copyright @ Wayne State UniversityIncludes Copyright Basics, Fair Use Checklist, and "Decision Tree" to help make decisions about how you can and can't use copyrighted materials in a university setting. http://copyright.wayne.edu/basics.php
Harry Fox AgencyHFA is the foremost mechanical licensing, collection, and distribution agency for music publishers in the U.S.
LIbrary Copyright Digital SliderUse this handy guide to help determine if a work first published in the USA is still under copyright or in public domain! Requires Macromedia Flash.
For background see https://blogs.law.gwu.edu/mcir/ and https://news.usc.edu/49112/online-music-archive-moves-to-usc-gould/. Resource formerly at http://ccnmtl.columbia.edu/projects/law/library/
PD INFO - Public Domain MusicA reference site to help identify public domain songs and public domain music . . . lists of public domain music, royalty free music recordings you can license, and public domain sheet music reprints.
SESACSESAC was founded in 1930 to serve European composers not adequately represented in the United States. Though the company name was once an acronym, today it is simply SESAC and not an abbreviation of anything. SESAC will represent the right for your music to be played in public. ... SESAC utilizes a selective process when affiliating songwriters and publishers, resulting in a roster of affiliates who have personal relationships with the SESAC staff.
Stanford University Libraries: Copyright & Fair Use"The Stanford Copyright & Fair Use site was started by Mike Keller, Vicky Reich and Tim Stanley in 1996 to support a talk that Mike was about to give ...Its emphasis is on copyright issues especially relevant to the education and library community, including examples of fair use and policies. Useful copyright charts and tools are continually added to help users evaluate copyright status and best practices." - See more at: http://fairuse.stanford.edu/about/#sthash.9MwUrat2.dpuf - from the Website.