This is a BROAD question looking at all the past build inventory of history and all the published images of ideas for the future.
That being said I always enjoy looking at big ideas architecture of the future, as much as we all know it will never happen there are always nuggets that slowly make their way into the minds of designers. Here is an interesting recent project: Paris 2050 by Vincent Callebaut Architecture. A proposal for multiple high-rise buildings with positive energy output (BEPOS). Comprised of eight multi-use structures inhabiting various locations within Paris, the plan strives to address major sustainability problems affecting each district, while providing key functions for the city.
