Mexican, Italian, chinese, thai, good ol' american comfort food, you name it.
Mexican- Go to Arturo's on Armitage and Western, it is open 24 hours a day, and the food is really good! Kitty corner to Arturo's is Maggie's Candies, it is an Old Time Ice Cream Shop it is literally 100 years old, the Beatles, and the Rolling Stones used to go for ice cream at Maggie's when they were in town.
Italian- La Scarola- It is one of the best Italian restaurants in the country, and the price is not bad 721 W. Grand Blvd. Celebreties eat at La Scarola whenever they are in Chicago, however you must make a reservation no matter what day of the week. Right next door to La Scarola is Richard's Bar, it is where the head of the Chicago Outfit runs business (kind of like the Soprano's Bada Bing, although Richards is not a strip club.)
Chinese- Ming Hiin for Dim Sum, there is one in Chinatown and one downtown. Best Dim Sum and the prices are not that bad.
Thai- Go to Manee Thai I believe they have three locations. North of Lincoln Park on Argyle street they have a Little Saigon, a really good Vietnamese Restaurant is Pho 777, it is relatively cheap and the food is great. I was once eating there and I turned around and Steven Spielberg was eating behind me. Funny think is, it is not a fancy restaurant, it would be the last place you would think you would see Spielberg.
The best American food in my opinion is L-Woods in Lincolnwood. Very good BBQ.
Someone was asking where are the best Ribs, I would chose L Woods.