Foreign Word
Dictsearch, the all-in-one dictionary search tool: search in over 170 different dictionaries from a single menu
http://www.foreignword.com/tools/dictsrch.htm
Glossarist
Searchable directory of thousands of glossaries and topical dictionaries containing terms and definitions on hundreds of subjects.
http://www.glossarist.com/
One Look
One Look
http://www.onelook.com/
Van Dale
Van Dale
http://www.vandale.be/
Your Dictionary
Yourdictionary - comprehensive authoritative dictionary, thesaurus, glossary and foreign language portal. every resource needed for language study in more than 300 languages.
http://www.yourdictionary.com/