Delphion
For international patent and us patent information, the delphion intellectual property network's patent search database helps businesses perform intellectual property monitoring.
http://www.delphion.com
Epo
Epo
http://www.european-patent-office.org/
Patent Cafe
Patentcafe provides artificial intelligence based patent search technology that finds prior art missed by boolean keyword search engines
http://www.patentcafe.com/