Business casual attire is considered nice slacks and a blouse. You can also wear khakis, but I wouldn't advise it for a job interview. They still look too casual. A blazer or jacket to dress up a business casual outfit would also look impressive to a recruiter. You always want to dress a little nicer in the job interview than you would in the job.
For an interview I would say nice slacks or a skirt, with a conservative blouse. A finishing piece like a sweater or a simple jacket is also an option. It is also important to remember to go easy on the perfume and cosmetics. Whether you wear flats or heeled shoes, make sure you can walk in them!
I work on a college campus helping students dress for interviews, and I always remind my clients that it is important to present yourself confidently, and let the focus be on your credentials. You want them to remember you, and not your outfit! So don't go too extreme in either direction -- khakis and a polo are a bit too casual, and a suit is too dressy!
Some people confuse the casual part and think jeans are tolerated! Do not do this! Simple slacks with a sweater top or a button down would be perfect. You are probably going to want to wear nice flats and no opened toed shoes!