I agree with Luke about Navy Pier, unless you want to catch a show at the Chicago Shakespeare Theater (they do more than Shakespeare plays), otherwise it's a waste of time. The art institute is my favorite. It's free on Thursday nights. If you're not over the let's go into a tall building, you may want to get drinks at the Signature room in the John Hancock building. Beautiful views of the city. I would also try to catch a Second City or Improv Olympic show.
Our PBS station hosts a show called Check, Please, where locals rate all types of restaurants in the Chicago area:
http://www.wttw.com/checkplease
Have fun!