U.S. Patents

USPTO Web Patent Database
http://www.uspto.gov/patft/index.html
Full text of all US patents issued since January 1, 1976, and full-page images of each page of every US patent issued since 1790.
U.S. Patent & Trademark Office
http://www.uspto.gov
Comprehensive United States patent portal. Official site of the United States Patent and Trademark Office.
MicroPatent PatentWeb
http://www.micropatent.com/0/patentweb.html
Offers fast document delivery from the world's largest digital patent archive.
Delphion Intellectual Property Network
http://www.delphion.com
Provides free access to data collections and patent information, including United States patents, European patents, patent applications, PCT application data from the World Intellectual Property Office, and Patent Abstracts of Japan.