Absolutely no dress code where I work. I try to be smart-casual, unless I know I'm going out to see a client, or they're coming in to see me, then I smarten up a bit. But I always keep a jacket at work, just in case.
I just have to hope they don't come in unannounced in the winter when I'm sat there in my sexy stripy fingerless gloves and a scarf because my office is super-cold
I'm not really a t-shirt kind of guy (except when scruffing it at home) anyways so I would at the very least wear a shirt and jeans.
I very rarely wear a suit (that reminds me I should look into getting a new one)
I always go see clients rather than them coming to me to save on the hassles
every time i've met a client i've just remained in jeans and a t shirt, obviously i ALWAYS look pretty nifty, but it makes it a lot less forced imo. people are more likely to open up and talk if they see if you in an approachable way.
obviously it does differ, just the people i've worked with i've never seen the point.