Delmonico's, Erie Blvd. Best steak/Italian restaurant in the city, IMO. Be sure to make a reservation though. Dinosaur BBQ is always good, and entertaining. Lots of cool bars and restaurants in Armory Square area. My favorite bar being the Blue Tusk. Lemongrass is also a tremendous Thai fusion restaurant in Armory. I take my wife there every year for her birthday.
If they have time, and are into SU sports, have them head over to the Manley complex and tour the Melo Center. Awesome exhibits for all sports, and you can actually look into where the men's/women's teams practice. Last time I was there my son and I got to watch GMac working on shooting.
On the hill, hit up The Varsity for a slice of pizza, and then Feagan's for their great beer selection.