Well I spent ~6 hours in Chicago last Tuesday and hurried through the the ArchiCenter, AIC, the Museum of Contemporary Photography, and the MCA (Museum of Contemporary Art). The ArchiCenter is cute, free, and across from the AIC (it is part of the Architectural Foundation), so you might want to pop in there. If you like Contemporary Art, I would go up to the MCA.
If you are there on a Saturday, check out the
Loop Tour Train. Did that once, and that was decent.
BillJ