http://www.ginoseast.com/
I know a lot of people like Giordano's too. We went to Gino's east first and now my kids won't go anywhere else when we occasionally visit Chicago. They loved doing the graffiti on the restaurant walls too.
They love this place for breakfast for some reason - I think it is the donut hole and ice cream they get:
http://www.loumitchellsrestaurant.com/