In my search for useful grammar websites, I've also explored those not specifically designed for classroom use.

Right now, I'm teaching a first-year writing class that is affiliated with an interdisciplinary first-year seminar in environmental science. Looking for articles to use in class, I came across this website http://www.counterbalance.net/. I haven't reviewed it in great detail but it seems like a good place to look for academic yet accessible conversations about interesting, contemporary issues.