Qtown is a great little tool to simplify creating a background city. It’s basic idea is based on the very handy 3ds max plugin ‘Greeble’ but more aiming towards building a city, below is a video describing its use.
Render Ready is a script that builds Architecture through a modular based approach. Simply by modeling a few modules you can create multiple configurations, and because the modules created have color maps, normal maps, spec maps, and an AO shader, rendering is as simple as placing a light and rendering an image.
KludgeCity is a procedural system for generating buildings — you only need one piece of geometry built in order to get started — something I refer to as a “footprint”. Once you create a footprint and load it into the system, simply change the variables in the KludgeArchitect rollouts, and press the Execute button. The building will be generated wherever the footprint is located in your scene, using whatever units you have set up in Maya.
MEL Procedural City Generator
This one looks absolutely amazing, check out the page, there are lots of videos demonstrations of not only city generation but of destruction as well. Unfortunately, the script doesn’t seem to be a product available for download…but pretty sweet!