Rome recently joined New York and Philadelphia as cities that offer free public wireless or wi-fi networks. Robin Good details Rome's network specifics in this report. As a Chicago resident I wondered if I had free city run wi-fi networks available in my area. The City of Chicago does not currently offer free wi-fi hotspots. I did a little more digging and found that there is a movement by the City of Chicago to run its own Wi-fi network and you can read more about it here.
The Chicago plan which is still in the developmental phase was based off of the wi-fi networks being installed in Philadelphia and other cities nationwide. Wireless transmitters placed in streetlights or other places throughout the city could make it possible to get high-speed Internet anywhere in the city.
Aside from public movements toward free wireless connections there are already a number of private companies offering free wireless Internet. I found that Chicago ranked second only to San Francisco in the top 25 free wireless hotspots offered by private venues. You can find networks in your area by going to Metrofreefi.com and selecting a U.S. location. If you are not in the U.S. you could us Google Local and search for Wi-fi. Wi-Fi Freespot and Wifinder list a number of Wi-fi hotspots across the globe.