Hugh Hefner would probably get some folks riled up...
Larry Ellison, 3rd richest guy in the world went to U of I for a couple years... (never did get a degree...from anywhere...)
Jerry Colangelo
Suzie Orman
Athletes:
Dick Butkus- I mean, c'mon...He's got a National award named after him...
Eddie Johnson (probably had the best NBA career of anyone not named Deron Williams, but his Illinois teams weren't great)
Derek Harper (same as Johnson. Odd stat: He and Eddie played exactly the same number of NBA games, 1199)
His Royal Frankness
I'd throw Luke Altmeyer in there as a crowd favorite right now...