Wolfram Alpha search engine now tracks flight paths, trajectory information. he search engine, which recently began incorporating data from the FAA can now, with a five-minute delay from real-time data, use a flight’s speed, heading and altitude to offer a projection of a plane’s position. A search for ‘flights overhead’ via the Wolfram Alpha web site or app will use your location to pinpoint flights that should be visible to you.

http://www.engadget.com/2011/11/19/wolfram-alpha-search-engine-now-tracks-flight-paths-trajectory/

Here’s a demo using Siri enabled iPhone