We live under a serious north-south airline corridor. Most days, when the sky is clear, you can look up and see contrails streaking high across the sky. Often you can see the actual planes as tiny white or silver dots moving through the sky out in front of the vapor trail. At night we see the airliners as blinking lights moving in the same north-south pattern.
Since there are no major commercial airports near us (or minor ones for that matter), most of the planes we see are up at cruising altitude. Every once in a while, if it's quiet, we'll hear the faint roar of jet engines a minute or so after a plane passes overhead.
There are some smaller airports in our region, mostly for private planes, and a military airport or two. Air force jets often zoom by us at very low altitude, scaring the bejesus out of us. There are also frequent police and medical helicopters that use the river valley as a corridor for their low-altitude flights.
I found a web site that tracks airliners in real time on a map. I can zoom in on my region and actually figure out which plane I'm seeing, the aircraft type, the airline, its altitude and airspeed, and it's origin and destination. Pretty darned cool, if you're into that sort of thing. Here's a link.