In all seriousness, you should never go to an interview in anything less than business casual - i.e. no jeans (wear khakis or something similar) and a collared shirt.
Even though I work for a professional company who is very casual (jeans/shorts/t-shirts are appropriate even for managers), we still expect people in interviews to dress nicely.
I held two interviews yesterday and while I don't know completely what they were wearing (the interviews were remotely via Skype), both candidates were wearing dress shirts, which I noticed right away.
Showing that you take pride in how you look is one small indicator to the prospective employer that you also probably take pride in the quality of work that you do.