Kad said: "I actually find it rather difficult to think of showtunes specifically about being American."
I think I understand what you mean (i.e., a showtune with lyrics that specifically indicate, "I am an American" and "I feel... [fill in the blank] about it!"
. Songs from historical shows like 1776 might be obvious first choices, but I prefer the direction you went with "Another National Anthem".
The subject line and description, "Americanness" are pretty open-ended. My litmus test is that if another country/culture can't relate, or relates to a lesser degree - it must be an example of "Americannness".
I think all of American Psycho is very representational - especially in regards to that time period.
I think songs from Altar Boyz and The Book of Morman are representational of specifically American views regarding religious beliefs.
Avenue Q is VERY American to my mind. When it was first announced that it was going to the West End, I was skeptical that it would play well because it IS so American. So... (as previously mentioned) I think "What Do You Do With a B.A. in Engiish/It Sucks To Be Me" definitely fits the topic of what it means to be American.
Also, "Great Big Stuff" from Dirty Rotten Scoundrels, "Much More" from The Fantasticks, most of the songs from Grease.