U.S. Copyright Office
http://www.copyright.gov/
The homepage has been created with the desire to serve the copyright community of creators and users, as well as the general public, and includes such topics as "What is copyright?" and the latest on orphan works.
U.S. Copyright Catalog
https://cocatalog.loc.gov/
Search for works registered and documents recorded by the U.S. Copyright Office since January 1, 1978.
WATCH (Writers Artists and Their Copyright Holders)
http://tyler.hrc.utexas.edu/
A database of copyright contacts for writers, artists, and prominent figures in other creative fields in the U.S. and U.K., run by the Harry Ransom Center and University of Reading Library. Also includes links to other U.S. and U.K. copyright resources.
FOB (Firms Out of Business)
http://tyler.hrc.utexas.edu/fob.cfm
A database of publishing, literary, and other firms that have gone out of business, run by the Harry Ransom Center and University of Reading Library.
Cornell University Library Copyright 101
https://guides.library.cornell.edu/copyright
Provides an overview of U.S. copyright law, including a Fair Use Checklist
Stanford Libraries Copyright & Fair Use
https://fairuse.stanford.edu/
Provides an overview of U.S. copyright law, including court cases