For those of you who like to track aircraft whilst mobile, you might like to try some of the available phone apps. Both Planefinder.net and Flightradar24.com have free and paid for apps for iPhone/iPad and Android devices.
The free apps can track planes on a Google map. For a one-off payments of a few Euros, the paid version adds contrails, aircraft illustrations, photographs, filters, searches and lots more flight and technical information such as routes, registration, hex codes and squawks. Check out the Planefinder.net website for current pricing and detailed specs.
Like Plane Finder, FlightRadar24 has free and paid versions. FlightRadar24 claims the most coverage for Europe with some cover in North America, Australia and New Zealand.
For latest pricing and specs visit the Apple App Store or the Android Market.