This is a British grammar site that has simple and clear explanations and exercises. If you read the examples and do the exercises it will help you learn and/or review all the English tenses!
Here is an excellent grammar site that will teach you all the grammar terminology you will ever need. Be sure to look at "Eight Parts of Speech" and do the exercises.
For French speakers: This is an excellent grammar site with explanations in French but everyone can try it!
Here's a new site I've just found. Each lesson has a video component. There are many levels - start with "Blue" - and new lessons are being added regularly.