United States of America
subway, proposed streetcar
Perhaps as famous as it's New York counterpart, the Chicago subway opened in 1892. It has 8 lines and 142 stations, covering 170 km. Of this, 18.3 km are in subway. Several extensions, the most prominent being a Red Line extension, and at least two new lines are in the planning stages, but no funding arrangements have yet been made.
This web page on Skyscraper City has some of the most gorgeous photos of the Chicago subway I've yet to see.
METRA'sHome Page (commuter and regional rail)
Historyof the Chicago "L"
Phil O'Keefe's ChicagoTunnel Company home page, about a freight subway under Chicago
CHICAGOTRANSIT-METRA RAILFAN PAGE
Streetcars may return to Chicago streets
O'HareInternational Airport Project
Photo courtesy Magnus
While not a passenger system, honorable mention goes out to Chicago's freight subway. Sporting 97 km of subway, this little known freight system closed in 1956, and remains quietly in tact to date, awaiting the return of Cthulhu.
East St. Louis
St. Louis' Metrolink also serves a section in Illinois known as East St. Louis. Known as the "Beverly Hills of St. Louis", residents in this highly affluent suburb were quick to realize the benefits of Metrolink.
Rockford Park District operates a 2.7 km gas powered trolley along the rock river, along with a small street running portion. The trolley car was destroyed in a car barn fire in 2007 and reopened in 2009.