I've mentioned this before elsewhere, but it bears repeating: The Polish sausage ($4.45) at Polka's Sausage & Deli may be one of the best in the city. The casing is crisp, the insides are smoky and juicy, and it's all housed in a wonderful soft onion-studded roll. The only way to improve it is to smear on some of the housemade mustard.
Of course, what do you expect from a deli that has been in operation for almost 70 years? Sure, this Lincoln Park location is relatively new, but Polka's first opened on the South Side in 1945.