Wikipedia has a pretty good overview, especially since it talks about regional cuisines like Chicago-style thick pizzas or Cajun cuisine: <http://en.wikipedia.org/wiki/Cuisine_of_the_United_States#The_origins_of_American_cuisine>
But I actually think fastfood is kind of interesting... Even perfectly radical-minded Europeans self-deprecatingly joke about their fondness of even the deadliest US fastfoods, like a Belgian I met who loves Kentucky Fried Chicken, or a German who needs to eat at McD's whenever he visits a new city.
And there are counterparts to US fastfood, like those Turkish döner shops which are ubiquitous in many German cities, and hotdogs in Norway.
Tayssir