Pizzeria Uno is the finest Chicago style pizza restaurant in the city. I find that funny since it is now a franchise that has spread across the Eastern US. For other location info and a menu check out http://www.pizzeriauno.com.
This restaurant is popular during normal dining hours, and the deep dish pizzas take a good 45min-1hour to prepare. Give yourself at least 1 hour before you are going to be starving to get your name on the waiting list. In order to speed things up, when you give the hostess your name, you also give her your order. This means that by the time you get a seat your pizza is already in the oven and you won't have to wait another hour to get it. Of course, you have to hang around for your name to be called, but since it is usually at least a 1/2 hour wait you can walk down Ohio to Michigan and check out a shop or two. You can also sit outside and have a beer or two. The Boston Lager is excellent.
A typical Chicago topping is sausage. My favorite combo is the Numero Uno with Mozzarella, chunky tomato, sausage, pepperoni, mushrooms, onions & peppers. The Chicago Classic is good too with Extra mozzarella, extra sausage, extra tomato, extra crisp crust, but may just give you a coronary.
The pizza is excellent, but don't let your stomach do the talking. This is heavy stuff, and the recommendations are usually about right. One Small is good for 2 people. Really.
Enjoy!