English Grammar Secrets
Great site with a page of explanation for the verb tense, with three different exercises to practice.
English Grammar Online
Great site with excellent explanations, quizzes, reading texts using the verb tense, and contrasts with commonly confused verb tenses.
University of Victoria, Study Zone Grammar Page
One of my personal favorite sites. Has great explanations for each topic, followed by two different exercises
Great explanations and tense contrast exercises.
Great site with verb tenses, clauses, articles, conditionals, etc. The explanations are long and complete, with lots of exercises at the end.
Road to Grammar
Very extensive lists of grammar topics with quizzes. If you click the "notes" section, there's a nice, concise explanation for the topic.
This site has very short (as in 1-3 sentences) explanations anda then a short exercise. But it has every single grammar topic imagineable!
This site has a very extensive list of grammar topics. Each one has a nice, concise explanation with lots of examples. You have to click over to their test section to get quizzes for the topic.
There are no explanations here, and the site only has prepositions, perfect tenses, and passive. But it also has a section on error recognition in sentences--nice for editing practice.
The information in this site is a little limited, but the games in the lower part of each page are really nice, particularly the grammar and vocabulary pages.
These are quite short grammar explanations, but without exercises. The site is good for a student who needs just a little bit more explanation.