Community Trade Marks On-line (http://oami.europa.eu/CTMOnline/RequestManager/de_SearchBasic?transition=start&source=Log-in.html&language=en&application=CTMOnline)
Database of European Community Trade Marks.

Intellectual Property Office Trade Marks Databases (http://www.ipo.gov.uk/tm/t-find/t-find-text.htm)
Covers UK trademarks only.

International Trade Mark Classification (http://www.wipo.int/classifications/en/)
The Nice Agreement classification scheme covering the kinds of products and services being trade marked.

Other trade mark databases and information websites (http://www.bl.uk/reshelp/findhelpsubject/socsci/intprop/tradmk/iptmdatabses/databases.html)
Concentrates on databases and official gazettes in trade marks, both free and priced, from anywhere in the world, plus domain names material. For other material, British and European sources are favoured. Maintained by the British Library