PixelActive have released a new version of their CityScape software. We are a picky bunch here at digital urban but the demo of CityScape is impressive, especially the ability to import native GIS data, OpenStreetMap and export to AutoDesk. Combine this with Unity and you have a powerful city creation tool, complete with traffic.
Admittedly CityScape is priced for high-end users ($19,000) – but the free demo is a blast and a must download for anyone interested in building cities.
See http://pixelactive3d.com/ for download and more details.