The Diner on Main Street is a good choice for breakfast-- classic greasy spoon that veers towards the Tex Mex. I prefer Taste of India on Alameda to Misal, despite the utilitarian decor. Tarahumara's is cheap, fast, popular, and pretty good Mexican food. It's on Porter and is usually mobbed on weekends. All of these restaurants are on the east side of Norman, the Last Picture Show side of town (as opposed to the west side-- suburban anywhere chain restaurants).
We've been talking about Norman in the thread "Coach's in OKC". As always, it depends on what you want. For bbQ, Van's Pig Stand, vegetarian The Earth, Misal of India has been there forever also. I like Legends for Sunday brunch. That's really all I know, it isn't my part of OK. Basic college town food. As chains go, Del Rancho is a local chain that is either great or awful. Their specialty is fried steak sandwiches. They have buttermilk on the menu.