If you crane your neck skyward, you may see the contrail of a jet or two. Should you want a more up close and personal look, Plane Finder 3D has just taxied up to the Google Play gate. This app tracks flights in real time over a number of cities.
The feature set is a bit light right now, but there is some real potential here. There are over two-dozen cities tracked in Plane Finder 3D, each with satellite imagery ground maps.