As Green as I've seen it anywhere in Florida, Key West is doing things right! We went to Key West on vacation this week. It's the first time I've been down there in about 25 years...and things have definitely changed for the better.
Once we arrived, I parked my car at the beautiful Santa Maria Suites (http://www.SantaMariaSuites.com) and didn't start it even once until we were ready to leave. This is because Key West is a 2-wheel "friendly" place. Scooters and bicycles everywhere...way more than cars. Little 50cc, EPA-friendly scooters, and electric cars and golf carts were the main modes of transportation there.
I was also very happy to see that everyone participates in recycling, and the appropriate trash bins were conveniently located in lots of places.