You'll get a bunch of different opinions and I'll probably get flamed, but hey, it worked for me.
Wear what you feel comfortable in. Dress professionally, yes, but be comfortable. If you're interviewing East Coast, go conservative. If you have an interview anywhere else, you have more leeway. I wore black dress pants, a long sleeved, collared shirt (striped, purple or blue, depending on the day), and a black vest with silver paisleys. I also interviewed in Tx in August/early September last year, and it was HOT - so I didnt wear a jacket (Im also female, which makes a difference). The biggest, hugest thing though, is....
WEAR COMFORTABLE SHOES!!!!!
let me say that again:
WEAR COMFORTABLE SHOES!!!!!
Yes, its nice to wear freshly polished dress shoes, but seriously - if you can up the comfort by sacrificing a bit in the way of looks, do it. No sneakers, of course, and still wear "professional" shoes, but so long as your shoes are the correct color, who's going to notice? (I can guaruntee you that admissions officers and interviewers wont give a hoot). Anyways.
Star