'Strine Decoded: Dictionary of Australian English: Dictionary covers Australian English, including slang, rhyming slang, Aboriginal English, place names, and animals.
A Dictionary of Slang Phrases: Every day phrases, idioms, slang words...A 8000-phrases up-to-date idioms and slang-dictionary.
A Guide to Irish Slang: From Arse to Maggot here is a full list of common Irish Slang
American Slang: Over 280 common American slang expressions sorted alphabetically.
American Slanguages: Talk like the locals in cities in America and around the world. The hick to hip translation guide.
Australian Slang Dictionary: Collection of Australian slang words.
Australian Slang Quiz 1: An Australian slang quiz with lots of quizzes about idioms and whatnot.
BuzzWhack: Buzzword-compliant dictionary provides definitions for business buzzwords, slang and jargon.
Civil War Slang: A page of a larger History site. Ignore the Angelfire popups.
Everyday English and Slang in Ireland: A comprehensive dictionary of Irish Slang with an "optimised for Print" page. Updated frequently.
Filters Magazine slang repository: slangin' up a fresh plate o' new words fo' that ace! Skateboarding and pop culture.
Internet's Recommended Slang Links: Large collection of links to slang-related dictionary sites for regional varieties of English. There are also links to specialized slang in English and to sites on slang in German and in Scandinavian languages.
Larry's Aussie Slang: Indexed slang and phrase dictionary.
Neologism Cliche Aphorism and Novel Language Pattern: Extensive list of new sayings, cliches, aphorisms, and neologisms. Has additional pages on related language matters.
PseudoDictionary: Covers slang, made up words, "webspeak", colloquialisms.
Roger's Profanisaurus: Glossary of sexual slang in English, mostly from Britain.
The Alternative English Dictionary: Part of a collection of on-line dictionaries of so-called "bad language".
The College Slang Page: Da Bomb: About the College Slang Research project at California State Polytechnic University. Contains glossaries and articles about the use of slang in a college environment.
The Online Dictionary of Playground Slang: An indexed dictionary providing many of the colloquialisms and slang words used, past and present, over the English-speaking world.
Twists, Slugs and Roscoes: A Glossary of Hardboiled Slang: combination of slang spoken by Philip Marlowe, Sam Spade, Mike Hammer and the Continental Op. When Cagney, Bogart, Robinson and Raft got in a turf war, this is how they talked.
Urban Dictionary: The vocabulary of everyday life.