It's hard to add anything new to the dialogue about James Dean as an American icon. But on a personal note, when Stand by Me helped usher in a period obsession with the 50's back when I was in elementary school, my sister and I both got cardboard stand-ups of Dean and Marilyn Monroe from our local novelty and sticker shop, CJ Kard.
Beyond the good looks that still stop hearts (really, has there been anyone quite like him since?), he had an undeniably impressive (but sadly brief) film career. He was a true rebel, not only on screen but with his daringly ambivalent sexuality, angst ridden method acting, and his literal live fast/die young attitude.
He also most best represented some of America's best fashion statements: white tees, denim, cowboy hat, fisherman's sweaters, bomber jackets, chinos and trenches.