Worldwide ( including PCT ) best free online patent search
The European Patent Office (EPO) has prepared the most comprehensive list of, and links to, databases of patents and published patent applications on the Web. These 30 million documents from all over the world are updated constantly and can be visited quickly. Go to Espacenet.
USA best free online patent search
For USA patents only, go to Webdatabase of USPTO ( US Patent and Trademark Office). It is updated weekly and includes patents granted (full-text since 1976, full-page images, as well as full-page images since 1790, and patent applications published since 15 March 2001.