When I was a kid I played this game on my Atari that was a simulation of being an air traffic controller. You got to direct planes for some pretty complicated scenarios, it even used the 4-bit audio to do speech synthesis so you could click on a plane and hear the pilot say something like "this is flight six nine one at four thousand feet heading two seven zero". Once in a while Concorde would come in at double speed or maybe a plane low on fuel that had to land immediately. The Chicago graveyard shift was the worst scenario, I crashed a lot of planes on that one.
Anyway, now you can see just how packed the skies over you really are thanks to Passur Airport Monitor. For instance how about seeing (with a 10 minute delay for security) all the planes overhead in an 80 mile radius from San Jose, or Los Angeles. Be patient it takes a little while to load the applet and fill the skies with data but once its there, cripes CJ that's a lot of planes! Click on an individual one to find out its flight number, plane type and altitude. Other airports are monitored and a list is available at Passur's site.