I'd agree with Big Will; I'm not sure there is a truly "original" style of beer from America, although the Anchor Steam Beer is unique.
Stylistically, there are some derivatives that are sufficiently different as to negate meaningful comparisons with their progenitors. Specifically, the west coast IPA style that incorporates Centennial/Chinook/Cascade/Columbus hops in obscene quantities rather than the traditional Goldings, Fuggles or other English varieties. The resulting "grapefruit" flavor is unmistakable. Same deal for Barley Wines, and to a lesser extent, robust Porters.
I was kind of thinking that I no longer really adored IPA's until I came across Dogfish Head 90 minute IPA
from Delaware. It is just fantastic. Huge beer at 9% ABV, and very hoppy with 90 IBU's. Yet amazingly balanced and drinkable. Very highly recommended. That's the real trick; to make a fantastically hoppy beer that does not taste ONLY like hop resin.