What are the spiders that build the huge webs in Chicago?

Question

They are only around in late July-August and make huge webs at night. The spiders themselves are nickel sized and brown/black mixed.

Answer 1

They are common garden spiders called Orb Weavers. They come in a multitude of colors, shapes, and sizes. Some are just stunning to look at. They can be as small as a nickel, however, nickel size it relatively small because most get quite large. They can look foreboding, but they are harmless and would rather not be anywhere near a human. I walked through a web one night and ended up with the spider on my shoulder. I never saw a spider move so fast trying to get off of me. Anyhow, don't worry about them. They do us a service by eating the insects that we'd rather not have around.

Here is a Yahoo picture search where you can see all the different species of orb weaver. There are pages and pages of pictures so you will probably be able to find your particular spider among them for comparison.
http://images.search.yahoo.com/search/images;_ylt=A9G_Rq08rNRGVzUAXlOJzbkF?p=orb+weaver+spiders&ei=UTF-8&fr=ks-ans&x=wrt

Answer 2

I would venture to say that is a wolf spider. Do you mean the triangular ground based webs, or the round ones? Must be a wolf tho.