We saw this on Chicagoist, and it came with a warning of the possibility of major time disappearance. They are right - consider yourself warned, too. Zillow has an interface based on satellite maps, that allows you to hover over Chicago and zoom in close enough to view specific buildings. Then you can start clicking on rooftops to find out what the pictured property is valued at.
Punch in a zip code to get started, and you can click all over your neighborhood or the one you are thinking about moving to. High-tech nosiness or valid financial tool? Both!