WorldChanging.com works from a simple premise: that the tools, models and ideas for building a better future lie all around us. That plenty of people are working on tools for change, but the fields in which they work remain unconnected. That the motive, means and opportunity for profound positive change are already present. That another world is not just possible, it's here. We only need to put the pieces together.
Appropedia - a wiki focusing on sustainability and international development. Includes technology and design that may be relevant to cities and urban design.