My town is on the approach for San Francisco, Oakland and San Jose airports, so needless to say there is always some air traffic going overhead. We're also not far from a major air force base and see a lot of big transports and bombers, and I always find myself looking up to figure out what they are. We've seen Airforce One fly over us a number of times over the years.
A really neat web site I found last year takes the guessing out of it. You can open up the following web page and see exactly what commercial aircraft are flying over you in real time. It gives the airline name, type of plane and flight plan, as well as altitude. Some flights have web cams in their cockpits and you can even tap into those. This web site covers the globe so anybody can use it.
http://www.flightradar24.com/#38.06,-122.59/9?&_suid=142004089372405930446959645852