Casual - black wing tips, black socks, very dark blue jeans (not black, not tight, not baggy), white button up shirt, black belt, watch with black leather band. Punch up the outfit with a dark grey blazer, a tie, or both.
Formal - Dark grey suit, Dark tie, white shirt, wing tips, dark grey socks.
90% of both of those outfit's are interchangeable. You can expand from there obviously, but this is a good start. Never wear a t-shirt. Don't over wear them or you'll look like you're in mourning.
I specified dark because it's slimming, but once you have that don't be afraid to add some color as you go. Get quality peices. Brooks Brothers, J. Crew, ect... Dress shirts should always be 2 ply. Patterns should always be classic (Houndstooth, gingham, ect...)