1-Language.Com ESL Center - an online interactive English site including help with Idioms in English OR Korean.

English Idioms and Quizzes - Over 1000 English idioms with definitions and examples, as well as hundreds of idiom quizzes.

Cobuild Idiom of the Day - A new idiom each day from the newly published Cobuild Dictionary of Idioms.

English-Zone.com Idioms - FUN idiom lessons and quizzes.

ESL Idiom Page - Hundreds of Idioms at the click of a mouse, brought to you by Dennis Oliver of the American Language and Culture Program at Arizona State University.