I was turned on to Flight Radar 24 by a friend a couple of years ago, and immediately bought the Gold Package!
If you are an aviation enthusiast and always have your eyes to the skies, I highly recommend it!
One of my most relaxing pastimes is to lay in my hammock under the grape vines in my back yard (which is right in the approach paths of two airports) and watch the traffic...
The fact that my wife has nearly turned our backyard into the Garden of Eden for me is icing on the cake...:)