You have two options for seeing Chicago from above: the Willis Tower (the building formerly known as the Sears Tower) or the John Hancock Center. The photo for this highlight was taken from the Willis Tower and the tall, black building in the background is the John Hancock.
The Skydeck on the 103rd floor of Willis Tower offers a 360-degree view as far as four states as well as the Ledge: four glass cube enclosures extending out from the building. The panorama is spectacular.
The observatory at the John Hancock Center has recently rebranded itself as 360º Chicago and added TILT, a glass observatory that projects forward during viewing.
Or, you can avoid the lines and admission fees of both attractions and instead enjoy an overpriced drink at the windowed Signature Lounge on the Hancock's 96th floor of the Hancock.