Kerpen, whose blog has been featured before in this space, writes that, at a job interview, you should dress comfortably and (at most) a little more formally than the rest of the office.
At a job interview, you're trying to show the organisation that you'd fit in there. If you show up dressed casually and everyone else is dressed more formally, you won't fit in. That's the easy part that everyone gets. But equally true is the converse: If you show up as a man in a three-piece suit or as a woman in a formal pantsuit, and everyone else there is casual, you also won't be fitting it. If a job applicant to one of our companies comes in a suit and tie, it shows that he didn't research the culture of our office — and it counts as a strike against him. Why take that risk?
As for what you should wear at work, read the post in its entirety: "How to dress for success today".