Well it depends. My day-to-day gear is usually jeans and a tee-shirt typically with some nerdy saying on it like my current favorites:
"Come to the Dark Side...we have cookies!"
or
98% Chimp
or
2+2=5 (For extremely large values of 2)
or (something my co-worker wore that I MUST have)
May the Mass times Acceleration be with you
(i.e. may the force be with you)
If I'm not wearing that I tend toward Dockers and polo shirts. When I'm going to 'step out' I like to wear a Brooks Brothers suit with a tie.
Cheers
Aj