English / French / Spanish / Italian / Chinese / Russian dictionary
http://www.leo.org/

German-English / German-Spanish dictionary
http://www.onlinewoerterbuecher.de/

Multilingual dictionary
http://www.pons.eu/

German-English-German dictionary
http://www.linguee.de/

Dictionary of synonyms
http://synonyme.woxikon.de/

Dictionary of the European Union 
www.iate.europa.eu

Multilingual technical dictionary (Architecture / Chemistry / Biology / Physics / Technology)
http://services.langenscheidt.de/fak/

Search engine for abbreviations:
http://www.abkuerzungen.de

Synonyms and associations
http://www.openthesaurus.de/

Glossary of the Federal Authorities of the Swiss Confederation (German / French / Italian):
http://www.admin.ch/glossar/index.html?lang=de

Search engine for encyclopaedias, thesauri, dictionaries and collections of quotations
http://www.lexikon.ch