allwords.com - english dictionary with multi-lingual search capability.
Casey's Snow Day Reverse Dictionary (and Guru)
DICT Development Group - simultaneously search several dictionaries using freely available client/server software.
Dictionary of American Regional English - specializes in regional words and phrases.
Dictionary.com - guide to dictionaries and reference materials on the internet.
Gaulish-English Dictionary - Gaulish spoken in Gaul and Belgium before the Romans conquered the land in 52BC.
Hypertext Webster Interface
Information Please - from the print reference database, offering millions of useful and interesting facts on a wide range of topics online. Also includes a dictionary and encyclopedia.
Lexical FreeNet - this program allows you to search for rhymes and relationships between words and concepts that might never have occurred to you.
Merriam-Webster Dictionary
Middle English Dictionary - offers a comprehensive analysis of lexicon and usage for the period 1100-1500, based on the analysis of a collection of over three million citation slips.
Mrs. Byrne's Dictionary of Unusual Words - unusual, obscure, and preposterous words.
Online English Dictionaries - collection of dictionaries and texts.
Online Rhyming Dictionary - retrieve a list of words that rhyme with a given input word.
Vocabulary of Alliteration - a dictionary of alliterative words, for use in writing poems, songs, and studying phonetic and phonemic syllable divisions in English.
WebSter's Dictionary 2.0 - spell checker for WWW documents. Enter a URL and this program will retrieve the document and spell check it.
Webster's Revised Unabridged Dictionary, 1913 Edition - an older dictionary, but with all the common words and a rich source of definitions of obsolete words.
Wordsmyth English Dictionary-Thesaurus
WriteExpress Online Rhyming Dictionary - find rhymes online.