Flight Radar 24 for the IPAD 2, NEW, is reduced this week On the Itunes Store to US.99 Cents. While the app is NOT perfect, it ireally makes a great companion to LiveATC.
Like LiveATC FlightRadar24 is based by a team of volunteers who feed Mode B transponder data. In the US they use both volunteers and FAA delayed by five minutes. Not many airports in the USA are covered by feeders AND the US has not required commercial aircraft to have Mode B transponders until 2019. Many US aircraft have mode B, most 747's, all 777's, some 767....
A real nice example of the beauty of this app and LiveATC is YSSY where almost all aircraft have Mode B and the coverage of the airport and the Sat feed is outstanding.
Try it and if you already use these apps, what do you think?