OK, this is all for Cincinnati, I have no clue where you live :P

24 Hour Diners: Waffle House, Denny's (although the only one in Cinci closed down )

24 Hour Fast Food: McDonald's, White Castle

Late Night Diners: Skyline, Gold Star

Other Fastfood: Taco Bell, Wendy's, Rally's

Also, if you wanna go crazy and spend a lot of money, whatever your favorite fancy restaurant is. All good options.