I'm not really that much of an expert, but I have an eye for quality and can occasionally nail a nicely done cheap painting. I am more of a film person, and couldn't stop talking when we had a running movie thread at this site.That's awesome! You should hit up some of the "Young Benefactors" engagements at local museums - you know your stuff and it's great networking opportunity!
The most famous American painting is probably Grant Wood's "American Gothic." The Hopper ^^^^, Whistler's mother and almost anything by Normal Rockwell are definitely in the top 5.