Free Patents Online
A well-designed site that allows you to search for patents by inventors’ names, issue dates, descriptions, etc. It is easier to navigate than the US Patent and Trademark Office site and claims to hold more data. The site also provides RSS feeds for patents by class—great for keeping up with a particular industry. Finally, it has a collection called Crazy Patents, which is great fun to browse when you are crazy for a break.
Google Patents
Search and read the full text of over 11.5 million patents in more than 100 countries, going back to 1790