Looks like Philly might be getting the 3rd largest building in the United States.  The new building will go up around 19th and Arch streets in the city.  It will be 1500 feet, that is about 600 feet taller than the new Comcast Center that was just completed.  Zoning restrictions are currently being changed in Philly to allow for a building of that height and size.  Just google American Commerce Center in Philadelphia and you can get their site and leasing info.