If we're talking about a chain restaurant, nobody beats PF Changs. Best food I've ever had from a mainstream dining establishment. The food is tremendous, the prices are quite affordable and the service has been among the best I've had and that's coming from a former waiter.
If we're talking about non-chains, the best italian food I've ever had is this little place in Carmel, California called Little Napoli. The ambiance is very comfortable, it's in the downtown area of one of the most beautiful places on the west coast and the food is unbelievable.
Oklahoma Joe's (in Kansas City) - My favorite BBQ place by far.
Free State Brewing Co. (Lawrence, KS) - Discovered this place my first semester at KU, and I love it. A great overall menu (Chedder Ale Soup is essential with every meal!), combined with a great location on Mass Street. Great place to go watch a game on a Sunday evening and have a few beers.
As far as steak houses are concerned, the two best places I found are Peter Luger's in Brooklyn and Donavon's in San Diego. There is a German butcher shop called Tip Top Meats in Carlsbad where you pick your own steak and they grill it for you. Steak and Stein are $10. Very good value that is tough to beat.
"Think of how stupid the average person is, and realize half of them are stupider than that." ~George Carlin
Mine has to be Steak and Ale, in South Bend. The best Prime Rib ever, and I have been to many a steakhouses. Their salad bar is off the charts as well. It is expensive, but if you ever come in for an Irish game, you must go there. They do have a dress code, but it is well worth your time. And, they have beer there!