A Punctuation game based on book by Lynne Truss entitled EATS, SHOOTS & LEAVES.  User-friendly format.           

Towards the middle of the page it tells you to connect to new
 link.  When you do, it does word and sentence levels, paragraph levels,  grammar and the 170+ grammar quizzes (basic sentence parts, verbs and  verbals, clauses and phrases, structural flaws, punctuation and basic  mechanics, pronoun usage, etc.).  Intermediate level.
            Actual link to the 170+ grammar quizzes mentioned above

 Purdue's OWL site:
Site is under construction but there is still a link to all the
 tutorials.  College approach but useful.

Daily grammar lesson archives on all parts of speech, parts of
 a sentence and mechanics
 click on the "Grammar" & "Writing" heading for a list of resources/links
 If you go to link that says English websites for students and once opened  scroll down to self-study grammar quizzes

Otherwise, link is
 An overview of important grammar and style concepts from top authors and  educators is presented.  Presentation format is topic by topic.