By far the best deep dish pizza in Madison. The pizzas I have had here, each many times:
1) Chicago Stuffed Pizza
2) Deep Dish Pan Pizza with Garlic Romano Crust
Both are amazing, and either one beats any other deep dish pizza I have had in Madison by a huge margin. 1) is truly massive and includes a top layer of crust (which is covered in an additional thin layer of sauce). 2) is my personal favorite because of the Garlic Romano Crust. This is not simply some flavoring sprinkled on the crust, but rather the entire bottom of the pizza has romano cheese and presumably garlic salt baked into it. It gives it an extra saltiness which is rather difficult to describe. It is amazing.
As others have noted, this place is quite hard to find. You will not see it from the street, so don't wait to turn until you do. Instead, pretend you are going to IHOP and go to the very back of the parking lot; there you will find Itzza Pizza.