The FlightTracker website tracks any US flights and some non-US flights. Just give it the airline and flight number or the departure and destination cities, and it will track the flight showing you a map (using Google maps) with the position of airplane. It also shows the scheduled departure and arrival times.
I know all this because my wife is coming home from the East Coast today. Her flight (UA 29) from JFK was delayed 1 1/2 hours taking off. She is now over West Virginia and is scheduled to arrive here at about 1:30 Friday morning.