As far as restaurants go it depends on what you're looking for. For a nicer lunch place I recommend Xoco. The chef there is Rick Bayless of Top Chef fame. You won't be disappointed.
http://www.rickbayless.com/restaurants/xoco.html For nicer Italian Rosebud is a good choice.
http://www.rosebudrestaurants.com/ Another decent lunch place is Rock Bottom Brewery. They only serve their own beers. And make sure you go to the brewery part and not RB Grille.
http://www.rockbottom.com/home There are a ton of great Sunday brunches as well. The only one that I've gone to in the Loop/River North area is Rockit and I highly recommend it. They have a great bloody mary bar.
http://www.rockitbarandgrill.com/ And if you're looking for Chicago pizza you're going to want to try to stay off the beaten path so you don't wait 3 hours for a table. The main places for that are Giordano's, Lou Malnati's, Pizzeria Uno, Pizzeria Due, and Gino's East. You might be better just getting it delivered if you're that curious. One last recommendation if you decide you want to venture out of the downtown area. For one of the best, most unique burgers you're going to want to hit up Kuma's Corner. Just don't go Friday-Sunday or during any traditionally high-traffic hours otherwise you'll have an hour wait minimum. I try to go on a Wednesday or Thursday at 3-4pm.
http://www.kumascorner.com/
