The U.S. Patent and Trademark Office (USPTO)
http://www.uspto.gov/

USPTO – FREE Searchable Patent Database
http://www.uspto.gov/patft/index.html

The Library of Congress – U.S. Copyright Office
http://lcweb.loc.gov/copyright/

The European Patent Office
http://www.epo.co.at/index.htm

Free Patents Online Database
http://www.freepatentsonline.com