The Gage is right across the street. It's more of a gastropub, with a bazillion different kinds of beer, but you can get cocktails too. And did I mention it's right across the street? :) www.thegagechicago.com
Also close by is the outdoor bar at Millennium Park - I think it may be owned by the Park Grill. Weather permitting it's a terrific spot for people watching and, taking in the sights of the lovely park.