Language Dictionaries Online: A Guide: Slang & Miscellaneous

"DARE does not include words that are commonly used throughout the United States, but rather focuses on the regional aspects of our language, documenting words, phrases, and pronunciations that vary from one place to another." --catalog summary

Edinburgh: Chambers, 2010. (Print version: Olin Reference PE 3721 .G677 2010 +)
An authoritative and extensive dictionary of slang words from the past five centuries up to the present day, from English-speaking countries and regions.

Open access online language translator covering many languages.

List of Emoticons frequently used online.

"2,500 English idioms, phrases and proverbs that we use every day, with their meanings and origins explained." [home page]

Acronyms of phrases frequently used online.

Unexpurgated ["not having potentially offensive or otherwise objectionable parts removed" - Merriam-Webster Dictionary], crowd-sourced definitions, and usage examples of current slang words and phrases.

Source for two services: A.Word.A.Day and Internet Anagram Server. A.Word.A.Day provides a new word every day with the definition, illustrative quotations, and audio pronunciation. You can subscribe to the e-mail version or just check the site. Archived back to 1994.