General

http://www.wiktionary.org/ – the Wiki-based Open Content dictionary
http://www.leo.org/ – German <> English, French, Spanish
http://www.italdict.de/ – German <> Italian
http://www.wordreference.com/ – English >< Italian Dictionary
http://www.oxfordparavia.it/ – English <> Italian
http://www.granddictionnaire.com – French, Latin > English
http://www.logos.net – Various languages and dialects
http://www.rae.es – Real Academia de Espana

Technical

http://www.fachlexika.de/technik/mechatronik/index.html – German <> English
http://www.wissen-elektrowerkzeuge.de/mdb/data/en/lexika/eopt/abrasives.html – major European languages
http://www.metallingua.com/szotar/feltolt/base/index.php – major European languages
http://www.didacticonline.de/int-en/services/online-dictionary/ – major European languages
http://www.axesindustries.com/glossaire.asp/lang/uk – major European languages
http://www.femfm.com/glossary.html?lg=italiano&bs=A – major European languages
http://lttwww.epfl.ch/teaching/files/Worterbuch_S-E-F-D-I.pdf – major European languages

Medical

http://medical-dictionary.thefreedictionary.com/ – Mono English
http://www.online-medical-dictionary.org/ – Mono English

Financial/Legal

http://tradition.axone.ch/
http://iate.europa.eu – IATE (Inter Active Terminology for Europe) Reference website for EU terminology and also financial and legal texts.
http://www.lai.com/glossaries.html – includes rare languages

Acronym finder

http://www.acronymfinder.com/ – Mostly abbreviations from English-speaking countries

Travel Links

Lonely Planet – Guidebooks, travel advice, country profiles and the Thorn Tree forum to discuss travel plans.