For every bright ray of sunshine there's a nearby shadow to be found and some of those shadows can make interesting photo subjects, either used in combination with the subject (top photo) or by themselves (bottom).
Part of the fun of using a shadow with its originating subject is that they usually mimic the shape of the main subject but with a slightly distorted twist. The trick to capturing both the subject and its shadow is finding a good vantage point for revealing them both, preferably against a simple background. I discovered this very graphic composition of a treasure hunter and his shadow on St. Augustine Beach in Florida by shooting down from the nearby pier. The thing I find interesting about shots like this is that the subject has no idea he's creating such a fun visual design.
The other option with shadows, of course, is to eliminate the subject and just shoot the shadow. In some ways this is more interesting because the viewer has to guess what the actual subject was and in some cases it's pretty difficult to tell. I found this interesting shadow at a highway overlook near Phoenix, Arizona and spent more time shooting it than the overlook view. Exposure for shadows is pretty easy, just take your reading from the brighter areas and let the shadows go black.