The Art Institute is the classic museum in Chicago that you won't want to miss. Michigan Ave/Adams St. In the summer, they are open free on Thursdays and Friday evenings so check their website for their free days when you arrive. Museum of Contemporary Art is near CHicago/Michigan and is amazing as well. Also, on Fridays from 5-8, there are many "gallery openings" in the River West area (Wells/Superior) where the galleries open their doors to their new peices and serve wine and cheese. You can check the reader (www.chicagoreader.com) for which galleries are opening on the day you will be there. There are usually 5-10 openings in a 1-2 block radius. Also, if this isn't enough, there is a private club called "The Union League CLub" down in the loop that you can call and ask if you can tour their art collection. One of the best art collections in the country.

Thanks--these are great suggestions!