English as a Second Language by Dr. Ron C. Lee is the most popular free online English-learning resource for ESL/EFL teachers and students throughout the world, and the most comprehensive, well-organized ESL/EFL resources Web directory.
Better at English: Free English lessons podcast based on authentic English usage, idioms, slang and everyday English conversations. Improve your vocabulary: Listen to English and learn English in just a few minutes a day.
250 free grammar exercises by level. Lower intermediate and upper intermediate level. Interactive grammar exercises for esl. Grammar tests and quizzes for all levels: elementary, intermediate and advanced.
Find lots of quizzes to test and refine your skills at "The Guide to Grammar and Writing," one of the oldest English grammar sites. It was created by Charles Darling and is sponsored by the Capital Community College Foundation, a nonprofit organization.