Saw this one a few months ago about a university professor who specializes in ants and has been dumping molten aluminum down anthills for some time now. Towards the end of the video, you can see his collection of castings and how varied the architecture of the colonies are from one species of ant to another.
http://www.youtube.com/watch?v=1IugvemOyZY
I also remember seeing one (possibly National Geographic) where they pumped a few tons of cement into a mega-ant hill and spent a few months excavating it. It was huge - like the size of a large house.
edit - found a segment on the concrete one:
http://www.youtube.com/watch?v=FLHAdwxLD-I