FlightStats is a great site for checking the status of just about any flight or airport. You can search by route, by flight, or by airport to find the information that you need.
My daughter flew from Arizona to MI on December 20, 2007. I was able to track both flights coming in.
After you enter the information of what you want to track, you get a lot of information. You'll see if the plane is on schedule, it will tell you the speed, altitude, miles flown from and to the destination, and even what kind of engine the plane has.
When she landed to switch planes, I was able to see that her 2nd flight was going to be early. That allowed me to get to the airport earlier to pick her up. This is an excellent, excellent site for both flyers and loved ones.
You can also check whether an airport is closed for any reason, or if there are any other problems. You can see their rating, scorecard, the security wait times, and more.
Other than tracking flights and checking on airports themselves, FlightStats also has a travel planner, travel deals, and other helpful tools.
If you are a frequent traveler, or if you have a loved one or friend coming to visit, FlightStats can save you a lot of worry and time. Best of all, it is free, so check it out HERE.