Spertus Institute for Jewish Studies (610 South Michigan Avenue) building. It's managed to do three things and do them all very well -- it filled in a gap in the streetwall, it presents an innovative and visually striking appearance, and it compliments its neighbors.
Part of its stunning visual effects involves the use of dots. Millions (billions?) of dots cover the crinkled facade to help regulate light and temperature as well as change the opacity of the glass.
This is a view looking out through the dots, northward, across Grant Park. As you can see, the picture is from this past winter, before the Blue Cross and Blue Shield Tower (300 East Randolph Street) finished its upward expansion.