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.