Chicago is reasonably bike friendly for a big city, fun to ride around and have a look. There is a great Critical Mass ride, 5:30 on last Friday of the month (June 29) in Daley Plaza. I'm not sure about the other cities. I don't live in Chicago so can't give you suggestions for shops but I do have family there and when I do visit, make sure it's the end of the month to ride Critical Mass. Up to 2500 riders, it's a blast.
If you go, I'll either be on a yellow/red/pink Klein with giraffe spots or a 1990 Attitude in green/white/pink. The ride goes on for hours so there is a good chance you could find me.