Move aside Leaning Tower of Pisa (or simply give in to your lean), because you're getting some steep competition from the PoroCity concept design. Of course, since it only received an honorable mention (which is still something) from this year's eVolo 2011 Skyscraper Competition, perhaps I'm being a little to hasty in my judgment.
Nevertheless, the PoroCity concept is pretty spectacular. Designed by Khushalani Associates, it was conceived with the purpose of providing some relief to one of the densest and largest slums in the world: Dharavi in Mumbai, India.
Inspired by the Sierpenski's Pyramid, the PoroCity concept deviates slightly to create an open air, connected, vertical environment that maximizes habitation.