We don't have diners in the Midwest. We have cafes. Not cafis (though those exist, as well), but the sort of place where, as kids, we'd get Green Rivers, burgers and big ole heaps of fries. Some are 24-hour joints, very much in the spirit of Jersey diners, with bottomless joe and similar quality food. (Generally, few Italian and no Greek items, though; the soup of the day might be knepfla, however, or chicken-wild rice. Ethnic dishes would tend strongly to be from Northern European cuisines.)
A lot of the restaurants people here would recognize as diners are chains -- Perkins, Denny's, Embers -- and they're generally not so fabulous. Perkins is especially egregious; it used to be terrific, but then got yuppified with salads and soups and god knows what all in bread bowls and muffins the size of your head, with checks to match. Ugh.
A tip for your travels -- in Fargo (I *do* assume you'll get to Fargo someday) , I'd go to Fry'n Pan, a small area chain with pie cases and waitresses who are extra-chatty and likely to call you "hon." There's also a real chrome-and-tin diner in downtown St. Paul, Minn., that's locally famous. I haven't been there in ages, but it used to be packed at lunchtime. It probably says something about the Midwest that I'm able to identify what is probably the only authentic diner in a neighboring state. There also used to be a fun-for-what-they-were chain of ersatz '50s diner-style restaurants in the Twin Cities called "Ediner" -- the first was in Edina, one of Minneapolis's posher suburbs -- but they were going down the tubes the last time I checked.
Steve Osvold
Denville, NJ
shewi@earthlink.net