Watch live airtraffic on flightradar24.com.
This site shows the live airplane traffic from different parts around the world. Only airplanes equipped with an ADS-B transponder (whatever that me be, but it must send some kind of radio signal) within the coverage area of the 100 receivers Flightradar.com has installed are visible on the map.
I like it a lot! Can watch this for hours . If I had the time .