Guide to Grammar and Writing: Fantastic resource for students and teachers; features an online grammar reference guide. More than seventy interactive grammar quizzes,

Self-Study Quizzes for ESL Students: More than 450 interactive quizzes covering grammar and syntax and a question and answer forum.

The English listening lounge: Practice listening to real English.And it's for free!

Study com's EFI : This site offers free English lessons in grammar , reading , writing,listening and speaking, as well as specialized classes