We have talked about it and given different opinions related to other topics but what communities have we seen that are sustainable? For reference here is a posting of communities that are both green and advertised as sustainable. The key is they already exist and we can see they are designed Green from the start. Living on the west coast I tend to like the one in Bend #3 and the one in Issaquah #6 because I still have family in Everett Washington and they would still be close enough to visit.
By the way I grew up when sustainable communities were more like the traditional native american Indian communities or even a Kibbutz so my perspective is slanted in that direction.