One thing you notice when you spend hours staring out an airliner window in flight is other airliners streaking past. Sometimes you'll see them headed in the same direction, flying roughly parallel to your path. Mostly, you see them go flashing by in the opposite direction (last week, we saw four in the space of about 30 seconds).
In the shot above, taken July 26, I was on an American Airlines flight headed west from Chicago to San Francisco. The local time, somewhere over Utah, was about 8:20 p.m. Suddenly, I spotted a jet heading north/northeast that appeared to have crossed below and ahead of us. It was there and gone in a few seconds, but I had my camera in hand and shot several frames before it disappeared.
Looking at the pictures afterward, I tried to make out the words and logo pained on the aircraft. After searching for a few minutes, I came up with an answer: Air Berlin. My educated guess, thanks to the airline site and looking for records on FlightAware.com, is that this was Air Berlin Flight 7499, about 46 minutes into a direct from from Las Vegas to Duesseldorf, and that our position at this moment was about 50 miles northeast of Price, Utah.
Below is a cropped image of the airliner, an Airbus 330. And below that is the original image--which among other things makes it clear how late in the day it was--before I started fiddling with it digitally to identify the plane.