There are a quite a bit of these floating around the Internet. Both Travelocity and Hotwire offer flight tracking services. I like the free FlightAware version of this service. I enjoy the flight information that it gives (estimated time to arrival, etc) and the various options that let you find the flight you’re looking for, even if you’ve forgotten the flight number.
The interface is easy to use, and the flight path map it creates gives you real time positioning of the airplane and the route it took to get to it’s destination. So let’s say your sister is coming into town tomorrow and you’d like to find out exactly how long the flight is delayed and exactly where it is.
That’s where FlightAware’s live flight tracker comes in 🙂 Let us know what you think or if you have another favorite.
There is also the tracker from FlightStats that comes integrated with a nice little Google map. Both of these services only show the flight on the map when the aircraft enters US airspace. I’ll keep my eyes out for a free one that lets you track planes in international airspace.