Sienna Miller wore this simple Calvin Klein frock for her appearance on David Letterman the other night, and when I saw her in it, I was just like... wow. At first glance, the dress is pretty basic. But that's the genius of it IMO. It's the sheer "nothingness" of this black racerback dress that makes it so chic. The lines in this dress are as clean as it gets in design, and I've always been a fan of the cleanest of lines.