I always felt there were three interpretations of the Kingdom of Heaven

1) the kingdom IN Heaven: not exactly the most interesting interpretation

2) a future world wide 'kingdom' on earth where everyone will live in peace and according to the will of God (whatever that may be), I think this is an important view: christians are supposed to improve this world an work towards creating the Kingdom of Heaven. I personally favor this view, since it humanizes the whole thing.

3)after judgement day the earth will be remade and the death shall rise and be judged, those worthy will be given an immortal body and live forever in this newly created paradise, the Kingdom of Heaven
(I probably got something a bit wrong here, but that's about the way it's supposed to go)