A good website for fashion tips in Wallstreet is www.vault.com
, go to the investment banking forums. PLenty of questions and answers there.
BUt while I'm at it I may as well help out, Minimum Shirt & Tie, may as well rock a jacket the first few days to get a feel for it. I have heard that some banks went business casual during the dot com days, though thats changed a bit lately.
Stick with conservative colors - pale pink, sky/french blue. Whites, and some patterns. No suspenders if you are just starting out. Actually no suspenders until you get established (they are touchy about that), no cufflinks or french colared shirts either.
BTW they are particular about who gets to wear pinstripes too