WIGLE - Wireless Network Community

http://www.wigle.net

This is an interesting application that "consolidate location and information of wireless networks world-wide to a central database, and have user-friendly java, windows, and web applications that can map, query and update the database via the web." As of today, there are 8 million wireless access points in their databases.
For example, if you want to see how many access points around the University of Baltimore, just enter the zip code on the page and get the map like that

http://www.wigle.net/gps/gps/Map/onlinemap/?addresscode=&citycode=&statecode=AK&zipcode=21201&variance=0.010&s=Show+Address