Online Dictionary Sites

Dictionary Building Software for Reporters
Software program for realtime reporters and captioners that lists many diverse vocabulary lists.
http://www.dictionaryjumpstart.com/

Dictionary Society of North America
An international organization of librarians, booksellers, translators, linguists, publishers, writers, journalists, and collectors. Founded in 1975 to further research in dictionary making, study, collection, and use. Member of the American Council of Learned Societies.
http://polyglot.lss.wisc.edu/dsna/index.html

Dictsearch
Search a variety of dictionaries including monolingual, bilingual, and specialty dictionaries.
http://www.foreignword.com/Tools/dictsrch.htm

Farlex Free Dictionary
Collection of dictionaries by subject including medical and legal together with free and subscription encyclopedias, in ten languages.
http://www.thefreedictionary.com/

Glossaries
Collection of more than 2400 links to glossaries and dictionaries.
http://frankdietz.com/glossary.htm

KnowPlay?
Simple and integrated access to dictionaries, thesauri, encylopedias, and quotation databases.
http://www.kplay.cc/reference.html

Research-It
Includes several dictionaries and a thesaurus as well as online tools for shipping and mailing, currency exchange, and language translation.
http://www.itools.com/

Webster's Online Dictionary: The Rosetta Edition
This database doubled with a metasearch tool extracts records from a variety of online and public-domain paper dictionaries, both general and specialized. It offers English definitions, as well as translations from/to a hundred languages.
http://www.websters-online-dictionary.com

Word Assault
Looks up multiple words simultaneously using several databases including Webster's, Easton's, Wordnet, and the Devil's Dictionary.
http://www.wordassault.com/