Los Angeles Public Library Science/Technology/Patents Department has the only complete United States patent collection in Southern California. They also have many patents from other countries as well as United States trademark and copyright records. See their Intellectual Property Resources guide for more information.
Databases for all United States patents issued since 1790 and recent patent applications. Users are advised to read the notices and follow the instructions provided, particularly regarding how to access and view the full-text images.
USPTO Forms provides many forms.
esp@cenet (European Patent Organisation) provides access to full-text patent applications from a number of countries, access to abstracts for others (such as Japan and China). See the site for further details.
Delphion Research includes patent documents from the United States, Europe and Japan as well as patent applications published by the World Intellectual Property Organization (which itself makes available an Intellectual Property Digital Library and other information about patents). Many features of Delphion Research are available only to subscribers or involve a payment. (Thomson Reuters)
Other useful patent sites include:
Google Patent Search. Many users will want to use this site's Advanced Search features. United States patents from 1790 to present except it doesn’t currently include patent applications, international patents, or U.S. patents issued over the last few months.
Guide to Intellectual Property Related Information and Services on the Internet (European Patent Office)
Patent Search Tutorial (University of Texas)