ESL Base - you need an account, but it's free to sign up and includes downloadable worksheets and ideas
Wyzant ESL Lessons & Help - good site for both teachers and learners; has lesson plans, teaching suggestions, and quizzes for learners
ESLpdf.com - grammar, idiom, and vocabulary worksheets
ManyThings.org - quizzes, word games, word puzzles, proverbs, slang expressions, anagrams, random-sentence generator, and other computer-assisted language learning activities
SpellingCity.com - allows you to plug in a list of words and create scrambles and word searches