1)   WordMaestro 1.50
The all-in-one thesaurus, English dictionary, anagram solver and word finder for Windows. Integrates seamlessly with other programs e.g. MS Word and Outlook.

 2)   WordNet-Online dictionary 2.0.1.2
WordNet-Online free dictionary and hierarchical thesaurus of English. Very easy to use! Definitions, synonyms, antonyms, hypernyms, hyponyms, meronyms, holonyms, derived forms and sample sentences.