Given that I work with our cloud program and in Austin I'm not as intimate with the alumni from Chicago, but one that I am personally fond of is http://www.giveforward.com/
They've crowd-funded over 125 million dollars toward medical expenses for people in need.
I'm a Chicagoan and and as jaredmck mentioned, there aren't any breakout successes. However, there are a number of companies are gaining steam like FoodGenius, Simple Relevance, and TempoIQ. Here's a link to the legacy Excellerate Portfolio: http://exceleratelabs.com/portfolio/
I think it's safe to say that's the answer - SpotHero is doing quite well and just raised a $4.5M series A, GiveForward as mentioned has crowdfunded a good amount of money for people's medical bills, and FeeFighters sold to groupon relatively early on. None of these are "breakout successes" to the tune of a 100M valuation, however.