Cook County's (Chicago's) Vital Records! They're here! They're here!
These are indexes - you still have to order the certificate from the Cook County Clerk office at $15/per, however, you can download the images (tiff files) immediately. The images have the words "For Genealogical Purposes Only" stamped on them, however, this doesn't effect readability much once you zoom in on a particular area of the image.
Records date from 1872
Birth certificates - 75 years or older
Marriage licenses - 50 years or older
Death certificates - 20 years or older
I may have found the site before they officially announced it...as I can't find a reference to it in a news search. However, I arrived there by clicking on the 'genealogy' link at the County Clerk site.
It doesn't say whether or not they've finished entering all the data yet, but I am having difficulty finding records I know have to be there. My great-grandmother Helen Deutsch died in 1958, in Chicago. I can't find her record.
The marriage of Adolph Rosenblum and Sarah Deutsch is listed in the Illinois Statewide Marriage Index, which goes up to 1900. That index says they were married in Cook County, on 2/18/1900. I can't find them on the Cook County site. I've even tried their soundex search.
So, it's not perfect. But it's exciting.
Note: As it was pointed out in the comments section, earlier when I read the "more info" and "FAQ" pages of the website I missed their statement that there are 8 million records, and they have only entered 6 million of them so far. This explains the gaps.