I usualy wear a polo shirt like stated and a pair of Dickies work pants...or simetimes I wear a matching dickies button up as well...
Seriously, one of the best jobs I ever had, I wore a T shirt and jeans shorts, with steel toe lace up boots to the interview! Of course I did not even know going in there was going to BE an interview. Shoot, I didn't even know they had the job opening, and I had never applied there! But I was pretty well known there, and as I was being unloaded, their boss came over to me and asked me to step into his office. Got hired right then and there.
I have worn jeans all my life except in the Army. If I wear anything else I feel like I'm wearing a dress or streaking. So all my job interviews were in blue jeans. Be true to yourself. If others cannot accept you as you are, find better company. (With shirts I have been far too liberal for my own good at times.)