Activities for ESL   
Dave's ESL Cafe   includes information on Idioms, Phrasal Verbs, Pronunciation, Quizzes, and Student Forums
English Club - ESL Quizzes
English Grammar Websites
English Grammar Secrets   
English Language Centre   
English Zone   Has sections on grammar, idioms, reading, spelling, writing, etc.
ESL Partyland   Quizzes on Grammar, idioms, etc.
Grammar from Edufind   
Guide to Grammar & Writing   
Idiom Connection   Everything about idioms!
Interesting Things for ESL Students   Vocabulary, Grammar, Quizzes, Listening, Reading, Spelling and more