Others

Synonym thesauri

This is a collection of some useful synonym and antonym dictionaries.

Synonym Finder and Thesaurus

Dictionary for synonyms, antonyms and definitions in English (AE as well as BE).
http://www.synonym.com/synonyms/

Roget's Thesauri

A collection of several thesaurus' editions for word lookup in British English.
http://www.bartleby.com/thesauri/

English Synonym Dictionary

This site provides a thesaurus in English.
http://dico.isc.cnrs.fr/dico/en/search

Thinkmap Visual Thesaurus

The "Visual Thesaurus" provides an interactive map of familiar words of a given term.
http://www.visualthesaurus.com/

Thesaurus

This site offers an English thesaurus.
http://thesaurus.reference.com

Alan Cooper's Homonym List

A collection of homonyms of the English language.
http://www.cooper.com/alan/homonym_list.html

Homonym list

myenglishgrammar.com provides grammar lessons, as well as example lists of synonyms, antonyms and homonyms.
http://www.myenglishgrammar.com/english/list-11-homonyms.html