chicagocrime.org: Chicago crime database
This is very cool example of integrating RSS with the Google Maps API to create a truly useful tool. In a nutshell — take crime stats, integrate into a simple interface that permits the user to browse by type (murder, assault, arson, etc.), address, route, date, zip code, etc. And then display the results on a Google map.
The applications are endless — find a safe neighborhood before buying. See if the neighbors are fond of domestic disturbances. Find a better way to walk to and from the subway stop.