It does have several elements to it, a judeo-christian ethos, a belief in the constitutional republic as envisioned by the founders, and a serious individualism rather than a collectivist one.
All of these qualities are of course being eroded by the Gramscian success of the left in defacing the common identity. A lack of proper civics education, a constant attack on religion and western values and the promotion of collectivist socialism is eroding much of the American "culture" but it's still there.
As I said before, I may not be able to describe it very well, but I know it when I see it.
As of 2004, Hip-Hop, reality shows and Wal-Mart. I have found that aside from about 10-20% of the country that could be considered "cultured" (ie seen movies other than Twister or Men in Black), most Americans, whether white, black or "other," tend to share they same respect for low culture. What is different now from say 30 years ago is that "middle brow" culture has disappered. A symptom of this is the decline of the family shi, er, "Sitcom" as a staple of television viewing.
Give me Sabado Gigante over Survivor or BET anyday of the week. Better yet, turn off the television and read a book for a change.