OmniDictionary is a Mac OS X client for retrieving information from network dictionary servers. It's pretty straightforward: type a word into the entry field, hit return, and the definition is displayed. Search any DICT protocol server for definitions, translations, thesaurus information, and more.
InstantTranslate makes it really easy to translate a selection of text in the application you are working in from one language to another language.
One World Dictionary by Ascendo is a leading multilingual reference tool for Apple desktops.
