If you're talking Chicago pizza, I recommend Lou Malnati's for deep dish, but you can't go wrong with Geno's (bearfan's suggestion) or Pequod's (Knick's suggestion). But, even better than all of these is the STUFFED pizza (crust on top and bottom, sausage swimming in cheese in between) at Giordanos. Eduardo's has good stuffed pizza too.
Those are all pretty touristy (well, not Pequod's). If you want to go where the locals go, a little farther North of the main tourist spots, I really like Stanley's on Lincoln and Armitage in the Lincoln Park neighborhood. Good comfort food restaurant in the back, and the front is a cool, casual bar, where my brother first met his wife. Maybe a younger crowd than you, but screw it. Another non-touristy suggestion for dinner is Mia Francesca, which is in Lakeview on Clark a short walk south of Wrigley Field.
Also, I highly recommend the Art Institute of Chicago, which is downtown near Grant Park. One of the great art museums in the world.
But again, I cannot emphasize strongly enough how essential a visit to Wieners Circle is to any Chicago trip, no matter how short.