Alinea is AWESOME if you are willing to drop a lot of $
http://www.alinea-restaurant.com/
Coco-Pazzo is an excellent Italian place!
Topolobampo and Frontera Grill are tasty mexican.
I prefer Gino's East if we're talking about Pizza...it's all about the corn meal crust!
Sopraffina has excellent salads and pizza for lunch M-F.
Potbelly is cheap and good toasted sandwiches.
Portillos is a classic for Hot-dogs!
Oh and i almost forgot, Paradise Pup for burgers is really awesome! That merkt's cheese is sooo good on it!
http://metromix.chicagotribune.com/dining/guides/summer/mmx-050614-chicago-burgers,0,4552171.story?coll=mmx-dining_summer_top_heds