Wordnet
http://wordnet.princeton.edu/

MultiWordnet
http://multiwordnet.itc.it/english/home.php

EuroWordNet
http://www.illc.uva.nl/EuroWordNet/

COMLEX Syntax
http://nlp.cs.nyu.edu/comlex/

Nooj / Intex
http://perso.orange.fr/rosavram/pages/noojpag.html

EDR dictionary
http://www.iijnet.or.jp/edr/