In this interesting video over at TED, Ellen Dunham-Jones discusses how suburbia could gradually be converted into more energy-efficient, healthier dense developments. I don't agree with everything she says. For instance, she complains about gasoline being too expensive, whereas the answer to our problems is constantly increasing the price of finite energy. I am also not convinced that we need all of that densely packed area, but she does also talk about re-greening.
The examples she gives are also not that radical. Simply converting the post office into a restaurant is not that exciting. I would be more interested in seeing shopping malls converted into mixed-use areas -- housing alongside businesses, with public spaces where people can just hang out without having to buy anything.
She nonetheless has some interesting ideas.