American cuisine can be essentially broken in to four parts:
1 - Fast Food
2 - Southern
3 - Old North
4 - Southwest
2 & 4, and 4 & Mexico overlap to a point, as does 1 & German. Stereotypically, however, "1" is most frequently associated with the US, most likely because it is easily industrialized, inexpensive and serves a useful purpose in an urban or automobile-nomad society.
"3" is the perhaps the most forgotten off all, but dishes like New England & Manhattan Clam Chowders and Maine lobster remain very common dishes well outside the Northeast. "4" is fairly memorable, and probably could be called to mind very fast to any foreigner, but as the unofficial Texas State Motto goes "It's a whole 'nother country down here."
"2" is perhaps the most unsung, and most unique. Also probably the best of American cuisine. Be it the Cajun side, the Atlantic side, the Black side (geography in the South is three-dimensional, partially dependent on color), or the Appalachian side, the quality of Southern cooking will resonate with anyone who has tried it. Though there is always some dispute as to which is which, and which is also outside influence, Southern cooking really is the best in the country.
Possibly the least impressive region in the country cooking-wise is the Midwest. Outside of Chicago, nothing significant in the culinary area can be attributed to them. California can lay claim to fast food, and the Northwest (2nd worst) can lay claim to a unique way of preparing salmon and a few other such things but I know of nothing that can be attributed to the rural Midwest.