DEPATISNET
Patent documents of the database of the German Patent and Trademark Office DPMA
depatisnet.dpma.de

REGISTER DPMA (formerly DPINFO)
Information regarding German patents, trademarks and registered designs
dpinfo.dpma.de

EPOLINE
Register of the European Patent Office EPO
register.epo.org

ESPACENET
Search for worldwide patent documents through the database of the European Patent Office EPO
www.espacenet.com

WIKIPATENTS
Extensive search, in particular concerning US patent documents
www.wikipatents.com

GOOGLEPATENTS
Extensive search, in particular concerning US patent documents
www.google.com/patents