I love the clean lines of this picture by Georgia O'Keefe. It is the Brooklyn Bridge. I can see a design forming just by looking at it. Simple and space but leaving the imagination to fill in the rest. I also liked this picture (scroll down and you will see the black bird and the sky).
The flowers of Georgia O'Keefe are lovely but this one stuck me by its simple beauty.
ETA: to change the pic to something that was not stealing bandwidth