There are many different dress codes for businesses. It might be casual, business casual, business professional, trendy, and so on. It depends on the company and the career you chose. A person who is interviewing for a finance corporate job most likely won't wear the same thing as a fashion assistant would (I would hope not at least). Here's a great article on different dress codes.
Since I was dressing for a finance job, I dressed more business professional. All of these items can be found at The Limited.
Your shoes should also be plain and match (preferably black). Your makeup should be basic, nothing too crazy. Again, like I said, this is for the finance world. I'm a big fan on J.Crew, Limited, Express, LOFT, and the like. Of course these places are all SUPER expensive, especially J.Crew. I try to only shop when I have a coupon or when items go on sale.
What would you wear to an interview in your field? Where do you shop?