DICTIONARY:  There are a large variety of online dictionaries. Dictionary.com is a standard dictionary with services including RSS Word of the Day, Translations, Medical, Legal and Foreign dictionaries.  Other online dictionaries include Free Dictionary and WordWeb.

THESAURUS: Thesaurus.com and Synonym.com both host very good thesaurus services.

ANTONYMS:  Thesaurus.com and Synonym.com both host very good antonym services.

REVERSE DICTIONARY: Similar to a thesaurus is a Reverse Dictionary.  Describe a concept of a word you do not know and this resource will find the word (if it exists).  Dictionary.com also hosts a reverse dictionary.

ETYMOLOGY: Understanding the Etymology, or word origin, of a word can be extremely useful in preparing for the vocabulary portion of a standardized test.  The first resource I will point out is Dictionary.com’s list of Word FAQs.  Etymonline hosts an extensive etymological dictionary.

VISUAL DICTIONARY:  VisuWords.com is a very useful application for visualizing how different words are connected (synonyms and antonyms) and are color coded based on word type.

WORD PODCASTS

OBSCURE WORDS