http://www.copyright.com
Copyright Clearance Center (US). Seek permission to reproduce copyrighted works.

http://www.csusa.org
Copyright Society of the USA.

http://www.lcweb.loc.gov
Copyright Office of the US Library of Congress.

http://www.marklitwak.com
Entertainment law resources for film, TV and multimedia producers by the author od 'Dealmaking in the Film & Television Industry'.

http://www.mcps.co.uk
MCPS Mechanical Copyright Protection Society. Music licensing.

http://www.mpa.org
Music Publishers' Association. Find out publisher /copyright information in order locate a piece of music or seek permission for its use.

http://www.musicadmin.com
Music Admin. Get recording and /or publishing rights cleared on any samples.

http://www.music-clearance.co.uk
Joan Eades. Help you find copyright owners and negotiate permission.

http://www.prs.co.uk
Performing Right Society. Information about licenses to perform copyrighted works.