There are of course numerous examples to choose from.
Most of the ethical decisions you'll hear about involving major corporations are bad: There's Enron's fraudulent accounting, HSBC's money laundering for terrorists, Ford concealing the hazards of the Pinto, and the collusion of several banks to manipulate the LIBOR, just to name a few.
But I'd actually like to take a different tack and talk about some major decisions by corporations that are not so bad, emphasizing the fact that ethical dilemmas arise in almost any large industry on a daily basis and can in fact be resolved well. Profits and ethics can sometimes come into conflict, but they are not inherently incompatible.
Morningstar Farms recently issued a voluntary recall of their Black Bean Burgers because they found traces of peanut in them which was not listed on the label.
I want to emphasize that they did not have to do this. It is not illegal to put peanuts in veggie burgers, and the fines for inaccurate labeling of this sort are quite small, especially when it is unintentional.
But Morninstar Farms knew that some of their customers might have peanut allergies, and would be harmed by the accidental peanut traces. They could have gone the way of Enron and Ford, run a cost-benefit analysis and decided that it was cheaper to risk the court cases than to recall the burgers; but they didn't. They saw the moral implications of risking harm to their customers, and refused to accept that outcome. They recalled the burgers, at great expense to themselves, in order to protect their customers from harm.
There are other examples of corporations making the morally right decision that I could talk about. There are always stories about health insurance companies not covering care people need---but we don't hear about the insurance companies that do cover people's care. There are always stories about the companies that pollute water, but never about companies like Pepsi that build clean-water infrastructure in Africa.
I don't mean to say that corporations are always sunshine and rainbows---they absolutely can do horrible things, and sometimes do. But I think we paint a distorted picture of the world when we only talk about the moral dilemmas that corporations get wrong. We should be trying to find out why some corporations make better decisions than others, in order to make more of the good ones and less of the bad ones.