U.S. Patents All patents from 1790- available here. Those before 1971 are only available as TIFF images.
Patent advice/Info Good site for all kinds of information and patent sites.
World Intellectual Property Organization, PCT WO patents with citations, abstracts and references supplied. WO applications since 1997- also included.
European Patent Office. Patent applications in original language from EP and WO may be found here. JP applications with English title and abstract are available. Images from PCT, EP and JP are available.
Free Patents Online: Free website, offering PDF versions of all patents from number 4000000-.