English Club English Grammar for ESL learners.
Many of these grammar lessons also have quizzes to check your understanding. If you still don't understand something, feel free to ask a question at the ESL Help Desk.
Grammar and Style Notes
Jack Lynch's grammar and style guide.
Ohio University's List of Grammar Links
All Levels; Many Sites
Sentence Structure: Simple Sentences
The parts of a simple sentence and how to put them together.
Teaching Grammar
Colin Mahoney's excellent article on how to teach grammar to ESL/EFL students.