Get a fully tailored suit. Spend as much as you can afford. Failing that, buy an off the shelf suit and have it tailored, a surprisingly inexpensive way of getting a suit that fits well. A good suit should be treated as an investment, feeling confident with your appearance helps immensely when interviewing.
Charcoal suit, white shirt, red tie, black shoes is all you really need to know, follow this mantra and you will be guaranteed to look good; you can then forget about the suit and concentrate on the interview.
If you want to get really suit-faggy read THIS thread, it goes into intricate detail.