http://a4esl.org/ Includes over 1,000 quizzes, exercises, and puzzles to help students studying English as a Second Language (ESL). The activities are contributed by teachers and include grammar and vocabulary activities.
http://www.eslcafe.com/ Resources for ESL teachers and students. Includes quizzes, slang, idioms, grammar lessons and much more! There is also a forum board for English Language Learners along with a job and resume posting site for the teachers.
Many links to resources and activities for students and teachers of ESL, maintained by the Internet TESL Journal. Includes grammar, writing, dictionaries, games, podcasts, bilingual quizzes in many languages, and much more.
(http://www.manythings.org/) Full of "word games, puzzles, quizzes, slang, proverbs," American English pronunciation exercises, and more to help individuals learn English. Some lists are designed for Japanese speakers.