Intellogist shows details on patent search systems (more than what is listed below) including the strengths and weaknesses of each.
Full-text of 7 million patent documents from US, Europe, Australia, WIPO, and counterparts in up to 60 countries.
U.S. Patents and Patent Applications -- Full-Text Images (1790 to date)
-Free AlternaTIFF Viewer for Images
Free Patents Online
Download patents from the U.S. and the World Intellectual Property Organization (WIPO)in pdf or TIFF formats.
Patents and Other Links (from the British Library)
Gateway to a wealth of patent information on the web, concentrating on world-wide sources compiled by the British Lending Library -- databases, tutorials, associations, publications, manuals, document suppliers and many others!