If you're looking for steak, hit either Gene & Georgetti for traditional old Italian steakhouse style great steaks, or Gibson's for great steak with fantastic star-studded atmosphere. Since I'm a Chicago native, I go to G&G.

For pizza, try Pizano's, either on State just north of Chicago (800 North block of State Street) or on Clark just south of Wrigley Field (~3400 block of North Clark). Pizano's is the original Chicago pizza recipe--the inventors of Chicago-style pizza (deep dish, not stuffed) were Mr. Sewell and Mr. Malnati. Mr. Sewell's pizza is made at Uno's and Due--as others here have said, not at all the chain store pizza. Mr. Malnati's pizza is made at the various Lou Malnati's pizzerias throughout Chicagoland (with my favorite the flagship at 439 N. Wells), as well as at both Pizano's, by Mr. Malnati's youngest son Rudy. Mr. Malnati (Rudy's mom) still spends significant time in the kitchen at the State Steet restaurant. As others have noted, get sausage on your pizza. I still rue the fact that the only place I can get a slice with real sausage on it (the crumbly stuff, not the sliced crap) is in Chicago.

If you're blind drunk, try the Weiner's Circle on Clark Street (~2600 north). The more blitzed you are, the better the dogs and cheese fries.

If you're looking for a unique lunch sandwich, try Ricobene's, on Lake Street between Wabash and Michigan. Their breaded steak sandwich is awesome, as are their cheese fries--among the best in town.

As noted by others, Trotter's is spectacular if you're on the company's dime (or proposing to your loved one).

Finally, if you're a fan of tapas, there is no better place outside of Spain than Cafe Iberico, in the 700 block of North Lasalle (just south of Chicago Avenue). They've been there for about 11 years (unfortunately, I left Chicago about 10 1/2 years ago, trading my 8 block walk to Iberico for the slowways of Silicon Valley), and consistently provide absolutely spectacular food at a great price. No complaints about service here either--the service is as good as it gets at any tapas restaurant.