Black and white photography has a way of letting the viewer really experience the image. Composition, light/shadow, texture and tonal qualities all become more obvious and important when color is absent.
Black and white portraits have an entirely different impact than color ones. When color is removed we are allowed to see into the subject, to really get a sense of emotion more so than if it were color.
Another way I look at it is if an image had a soul it would be black and white. Stripping away the window dressing (color) allows you to get down to the real essence of the image. (OK, that sounds a little out there but you know what I mean)
Below are some excellent examples, Enjoy!