3541 N. Clark
773-880-0199 or iochicago.net
It's not hard to find improv in this town, but every Wednesday at 8 PM in its Cabaret theater, I.O. has a free show, and unlike Second City and elsewhere you don't even have to pay for the one before it to get in. Two rotating teams and one regular group of vets--Carl & the Passions--perform for about 30 minutes each. All are funny enough that I would pay to see them again. And I hardly ever pay for anything.