This information is provided by the University of Maryland University College and is laid out in a very accessible format. It notes specifics and also gives an overview of the rules.
This is a great website which explains copyright law and how you can register your own work! This site is provided by the Copyright Society of America and is one of the clearest explanations of the rules that you will find anywhere.
This site is maintained by the Copyright Clearance Center. You can learn specific information about copyright law and search by title to find out if a work is covered. For a fee, you can pay for use through this site. You can also register your own works.