Here's a pretty interesting one.
Through what seems like (according to this article) no force or coercion from legalities (But with incentives) Mexico City has become one of the most environmentally conscious cities around. I'm not familiar with the air-quality scoring system, but I know that a score of 200 is way bigger than a score of 50. And I know they're not done yet.
http://green.blogs.nytimes.com/2013/...urns-a-corner/