In these days of reduced services at the airlines, it is often difficult to find an accurate arrival or departure time if your flight is delayed. I have used FlightStats for years. It has a web page as well apps for Android, iPhone and Blackberry. I am currently using FlightStats for Android.
FlightStats will enable you to look up flights by flight, airline or Airport as well as track and save trips. It will show you the current status of your flight as well as gate numbers. You can also track your flight on a map complete with speed and altitude information. Flight stats also will list all upcoming departures from the selected airport if you have to start looking for alternatives in the case of a flight cancellation. Take a look at this video overview.
All in all a very handy app for even the casual traveller. Go to the FlightStats site and click on the Mobile tab for ordering information. The price ranges from free to $4.99 depending on features