Here's the results of a report by the folks at ethisphere. Their pick for the top urban sustainability centers by 2020:
New York City
Then they list the top ten sustainable cities under 600,000:
Copenhagen, Doha, Edinburgh, Helsinki, Oslo, Portland (OR), Reykjavik, Victoria (CAN), Wellington (NZ), Rotterdam.
Major energy using nations not on this list at all: China, France, Indonesia, Italy, Japan, Russia. The entire continent of Africa has only one city listed, ditto for South America. Canada and the U.S. each have two cities listed. Until Scotland becomes independent, the UK can also claim two cities.