I’m trying to create an array of buildings (simple rectangles) for my simulation. I want to have these blocks to be assorted into a grid with somewhat random heights, like what would be a city. I’ve tried the array modifier but I can’t get it to do what I want, can someone help me do this?
http://www.blendercycles.com/tutorials/city
You can look at the tutorial or download Suicidator City Generator from there. However, Suicidator City Generator uses 2.49, but you can always export the city into an obj file and use it on a different blender. 
Or you could do it like everyone else and make rectangle after rectangle after rectangle… 