Let's forget about hot dogs for the moment. Could it be that the most common sausage in America is the Italian sausage? Perhaps it's the prevalent Italian influence on American cooking, but Italian sausage is called for more often, and available in more butcher cases in the country, than any other.
The sausage tradition in Chicago, however, owes more to German cooking (and closely related sausage traditions, like Polish). Our well-known, old-school butcher shops specialize in smoked and cured sausages, and the fresh varieties tend to be more finely-textured kinds of sausage that you find in Germany. They're not always so great at making truly great Italian sausage.
Bari Foods on Grand Avenue is an exception. It is firmly old school and firmly Italian; the service is appropriately gruff and straightforward. But as often is the case with these kinds of places, you're not there to be pampered. It's worth enduring a little rudeness because of the quality of the product.
And the fact is, if you're looking for a great Italian sausage—coarse-ground pork stuffed into a hog casing, flavored with a little fennel and sometimes herbs—then you can hardly do better than Bari. They make it in-house, it's a "family recipe," and it's delicious.
Of course, the main reason people stop into Bari is for their incredible and inexpensive sandwiches. The Bari sub is one of Chicago's better-known Italian Sub specimens, made with high-quality ingredients sliced fresh.
I've had and loved their Italian sub, but I was on a sausage mission this time. So I opted for the sausage sub, which is served simply with roasted peppers, and, crucially, on the best Italian sub bread in the city, from D'Amato's bakery, which is literally next door. It lets the sausage stand out, which is simple: with just a touch of chile flakes and plenty of fennel. My only suggestion is to eat it right away, because the heat from the sausage tends to soften the glorious crust of D'Amato's coal-fire oven bread.
Italian sausage is easy enough to find in the case of almost any grocery store. But if you're after a version that's made more masterfully—not overly fine, seasoned with refinement—stop by Bari and buy it fresh or have a sandwich.