I had a go with City Engine and it's a great tool but unfortunately since ERSI bought it my license no longer works. An annoying shame.
Houdini has some great procedural city building tools but you really need to learn Houdini first (which I am still trying to find the time to do). Also Houdini cities are destructible!
There is a addon for Blender called SceneCity which looks promising.
https://planetside.co.uk/forums/index.php/topic,26235.msg261087.html#msg261087 Development is slow but it is affordable and Blender is FREE.
I don't really know of any other city building software, some game engines maybe?
I love to know if there was any, especially a plugin for lightwave!
Of course the main issue (for us Terragen users) is that any generated city will have to be exported as a large model and once it is in Terragen it no longer has any "procedural" properties.