Leslie, being from Indiana originally, I got to visit Chicago a lot. The Art museum that Albea mentioned is fabulous, and the Shedd Aquarium and Museum of Science and Industry that Rachel mentioned are definitely must sees. I also enjoy the Museum of Natural History a lot. There is a planetarium nearby also. Definitely take advantage of the public transportation, that way you don't have to worry about driving and directions. Also, depending on where you're staying, they usually have maps to places that are within walking distance of your hotel.
Craving some good food?? Take a cab to Lowry's (a little pricey, but well worth it if you like Prime rib)for the best prime rib you'll ever eat. If you're into Italian food, the Italian Village is quite tasty too! I always have to eat at both places when I'm in Chicago!

Enjoy your trip!
Karen