Dlb, are you going to be in the Loop? If so, I've got boatloads of ideas for you.
* You could lose a day, easy, in the Art Institute of Chicago and still feel like you haven't seen everything.
* Go to Millennium Park and walk around (and under) the Bean. It's pretty cool. You'll be close to the lake there -- if you've got your woolly undies on, you could walk to the shore. (Trust me, you will *need* your woolly undies in Chicago in November....)
* While you're out looking at public sculpture, go see the Calder at Federal Center Plaza and the Picasso at Daley Plaza.
* The Field Museum has a good Egyptology exhibit -- lots of mummies.

Farther south along the lake, in Jackson Park, the Museum of Science and Industry has a bunch of cool stuff -- a coal mine exhibit, a real U-2 sub you can tour, and a giant model of a human heart you can walk through. Near the Museum of Science and Industry is the Shedd Aquarium, which used to be kind of dorky but which I believe got a facelift not long ago.
* If you walk north on Michigan Avenue across the Chicago River, you'll pass the Water Tower that survived the big fire allegedly caused by Mrs. O'Leary's cow.

Just past that is Water Tower Place, a multi-story shopping mall. In fact, there's shopping all along Michigan Avenue.
* There's an observation deck atop -- um, well, it used to be the Sears Tower but I think it's called something else now. Anyhow, it's right next to Union Station. (My brother used to work on the floor right below the observation deck, so the girls and I got to appreciate the view for free.

)
* Another idea for just walking around: You might be able to find one of those laminated "Artwise Chicago" maps at your local bookstore before you go. Chicago has amazing architecture, and I believe many of the best ones are listed on that "Artwise" map.
* Restaurants: The original Pizzeria Uno is, uh, somewhere in the Loop. I found a teashop I liked on the north side of Federal Center Plaza last summer. That's about all I know -- ask Damelon, he may have some better ideas for food.