Here are the few that I saw while doing a research field trip for my space. They're all in the loop, or nearby:
TechNexus - very nice place (kind of corporate), productive and full. Lots of moderate-sized rooms, which seemed helpful
OfficePort - a little more bare-bones (lots of concrete), mostly 4-person team areas. Nice folks.
1871 - INSANE space. 50,000 sf. Also an incubator & mini-school. Has an intelligentsia coffee bar in it and is sponsored by everyone under the sun. Visited by the UK Prime Minister while he was in town.
Enerspace - Very nice new space. Emphasizes wellness + productivity.
The COOP - Early pioneers. Design company runs the space and develops
desktimeapp.com. Super nice space and people.
Chicago has a good coworking ecosystem, but the suburbs are waaaay lagging. Thus, my soon-to-be-announced space in Waukegan, IL.
-Brendan