Tyler Green has a post about the imagery of the American flag, how it's used/abused by both political parties. He has asked for suggestions. My most vivid memory of the flag is Stanley Forman's 1976 Pulitzer Prize-winning photo (above) at an anti-busing demonstration in Boston. That probably falls into the photo-journalism category but - how powerful. Others that come to my mind are shown below.
Art that uses a recognizable symbol, like the U.S. flag, does so best when it calls into question the conventional meaning of that symbol. This is not to say that it has to be necessarily a negative meaning, which is a temptation for many artists, I suppose, when treating something like the U.S. flag (like James Rosenquist's recent Xenophobic Movie Director, or Our Foreign Policy). It may be too obvious for Tyler's survey, but Nam June Paik's Video Flag (1985-1996) immediately came to mind. It is a much more positive version of the concept than an earlier form of the work, Video Flag Z, owned by the Los Angeles County Museum of Art and now unable to be shown. Both subvert a symbol we take for granted by assembling the symbol out of images that incarnate the shifting meanings of that symbol for many people. (My love of Paik's work has nothing to do with the fact that he was a musicologist, either.)
In a similar vein and perhaps less obviously, Romare Bearden's Roots Odyssey (1976) uses the symbol of the flag to represent the shores of the United States as the destination of a slave ship. Once again, the symbol does not necessarily mean what you think it does, and it may have different meanings for different people. The United States is a large, multifaceted country with a complicated history, and the flag has greater meaning if it is not a one-dimensional symbol. (Related: David Hammons, African-American Flag, which the MoMA curator Connie Butler already picked for Tyler).