Realtime rendering has moved on a long way in recent years – a prime example is Lumion® a real-time 3D visualisation tool for architects, urban planners and designers.
Suited for creating videos, still renderings and live demonstrations with a quick turnaround Lumion provides high quality output and best of all there is a free version, the movie below provides a look at version 1.0:
In terms of cityscapes Nano 3D Virtual Studio entered the Lumion architecture visualization competition 2011, the results are impressive: