BBC Learning English
http://www.bbc.co.uk/worldservice/learningenglish/index.shtml

UsingEnglish.com - A large collection of idioms listed alphabetically, with brief definitions.
http://www.usingenglish.com/reference/idioms/

Free weekly newsletter with a vocabulary quiz with a business focus (The quiz is often on business idioms/expressions seen in the news)
http://www.business-spotlight.de/our-products/newsletter

Self Study Idiom Quizzes
http://a4esl.org/q/h/idioms.html

The Idiom Site - definitions of popular idioms
http://www.idiomsite.com/

Nik Peachey's Daily Activities - tips for self study

http://daily-english-activities.blogspot.com/2009/06/find-idioms-in-everyday-language.html
http://daily-english-activities.blogspot.com/2008/10/learn-some-cliches.html

Artilce and classroom activities on
puns, metaphors and idioms
http://www.hltmag.co.uk/aug08/less02.htm


Searchable index of idioms expressions
http://rea.ccdmd.qc.ca/ri/Expressions/debutEN.asp?sw=1024&sh=768

Online idioms and expressions board game
http://www.english-portal.com/games/walk/walk.htm

Vocabulary building fun and games
http://www.vocabulary.co.il/games2/unscramble/index.php
http://vocabsushi.com/
http://www.wordahead.com

Weekly worksheets for colloquial expressions
http://www.splendid-speaking.com/products/wotd/index.html

Teaching idioms using movies - transcript of 'Monsters, Inc'
http://www.script-o-rama.com/movie_scripts/m/monsters-inc-script-transcript-pixar.html