Concerned that Big Brother might be watching?? How about anyone with an internet connection...
FlightTracker - Flight tracker for aircraft transmitting ADS-B
planefinder.net - Real Time Live Air Traffic Flight Radar
Flightradar24.com - Live Flight Tracker!
RadarVirtuel.com
Granted, the coverage is limited to areas where someone has connected up
a USB ADS-B receiver to their PC, but as the more major of those links show, the coverage is already fairly significant...
As a sidebar, interesting that the planefinder one has added Volcanic Ash Cloud monitoring as well
