Just thought I'd share a flight app we've used for the last year or so, which also has a website. It has been helpful keeping us informed.
FlightAware has an app wherein you plug-in airline name and flight number. The result you get is pretty accurate (we've put it within a couple of minutes), and it tells you when a flight is expected to depart, when it departed and the estimated arrival time. You can also click on a map and it will show you the plane's progress on a map. It also gives info that is interesting, but we don't really need such as type of plane, speed, altitude, and route. You can even click on a flight log which shows ascent and descent.
Today, I found their website, flightaware.com. The piece of info which was interesting was that the flight result showed an estimated cost for that particular flight. I clicked on it and got more info.
This app has been useful for when we are at an airport waiting for the flight to come in on which we will be boarding. When there have been delays, we were right on top of when our plane would arrive.
I know there are probably other websites with this information as well, but this one has been helpful for us.