The largest Internet companies in Chicago

I spend a few hours a week meeting with people who are either a) looking for a job at an Internet company or b) looking to start one.  I always run through a list of both large and interesting (sometimes they are actually both!) Internet companies.  My definition of an Internet company is a company delivers the majority of their service and product over the Internet.  I will create a separate list of folks like United Airlines, Hyatt and Sears who are using the web in significant ways to drive sales. My bias with this particular list is toward the "consumer Internet" because I know less about the agency, consulting and b2b space, so please add some comments about who you would add.