Opaque Priceline/Hotwire often gets you the Hyatt Regency on Wacker cheaply.
Search this forum for whatever you like, using keywords. There is a ton of info already posted.
Theater
Museum
Tour
Shopping
Architecture
Art
Science
etc.
I would suggest the Art Institute, since you'll be at the Bean next door. People come here from around the world to see it. Also Millennium Park (where the Bean is) is considered a great example of urban landscape architecture and worth exploring if the weather is decent.