Certainly twitter and facebook, and there are others like Khan Academy, but what are some other startups that qualify--or at least have the capacity to qualify--as world changers?
I'm hopeful for Bank Simple, Square, and others trying to fix up the way we pay each other and take payments. Having operated a small business (salon) for the past two years, merchant accounts, payments, etc are all a total black box and you have no options/control.