Traditional, traditional, traditional. Even going out on a limb with a light suit is a bad idea. Corporations want to know you are going to respect them. While you still want to look well-kept, you can feel comfortable. But don't get carried away - that short little green number you picked up last weekend isn't going to fit the bill.
Ladies can strut their stuff in a sweater and pants or a long skirt, for example.
As for the gentlemen, you can forego the tie, but nice pants and a dress shirt are still your best bet for impressing the big bad interviewer. That is why it is crucial to pay attention to the details on interview day. For starters, leave more than plenty of time to get everything organized and to get where you are going. It is amazing how much better things will go if you don't feel rushed or frazzled when you walk in the office door, and you can never predict a freeway jam, broken elevator, or overturned truck of wild midgets. Better to get there an hour early than even five minutes late.