A quaint little Starbucks located close the Prudential building. It's situated in the Radisson Blu Aqua Hotel.
Nice meeting point if you're going to Millennium Park or Michigan Avenue. The Starbucks doesn't have it's own seating, but you can sit in the Hotel's waiting area, which is very nice (and it has a long fireplace stretching across the wall, which is pretty cool).
Address
221 North Columbus Drive, Chicago, 60601, Illinois, United States of America