I follow a blog that is written by an air traffic controller. He introduced me to this site. It is called Flight Aware. You can track flights (with a slight time lag) across the USA. You can track according to operator, aircraft type, and destination/daparture point. It will show you the invisible side of air operations in the USA. Now, you can look up in the air and have a better idea of where that airplane is going and possibly where it is coming from.