Haiti is rapidly shifting from being among the most poorly-mapped populated places in the world to being mapped at high resolution in near-real time. This is a result of a remarkable confluence of several international, open-source mapping projects, all of which are focused on the development of maps that can help those who are helping Haiti. Clark Boyd describes the efforts on Public Radio International.
Explore Port-au-Prince on the Dutch Open Street Map. Spend some time exploring this map in detail; it shows collapsed buildings, hospitals, obstacles, and temporary encampments -- on the viewer's choice of street maps satellite imagery. These maps can literally save lives, by helping aid workers understand where the needs are, where the resources are, and connections are most easily made between the two.