Police Scanner for WP7 streams police bands the world over
The demo video (below) includes such cities as Chicago, IL.; Los Angeles, CA.; Miami, FL.; New York, NY.; Memphis, TN.; Columbus, (OH.); Queensland, Australia; and Waterloo, Ontario.
There isn't a full list as of yet, but there are reportedly over 2,000 feeds available. There is also a reference guide for police and emergency codes, like '10-4' meaning 'Okay', etc.
Police Scanner is from Carmelo Milan, the developer of PhotoWiz. Milan's PhotoWiz app for Windows Mobile simplifies the device's camera by optimizing the camera's settings for different light conditions and subjects.
source: wpcentral (formerly WMExperts)