My previous work place was the very fancy headquarter office of a large engineering firm and the dress code was business casual - khakis, polo shirts, etc. with jeans and sports shoes only on Fridays. This was mostly because a lot of the younger engineers had to be on the field often and needed to dress comfortably. However, my boss at the time was very conservative and always wore a shirt and tie. I tended to follow his example and mostly wore skirt or pants suits with high heel shoes (which I LOVE). Really the most I ever dressed down was switching the suit for a skirt and sweater. He and I never went out to any of the field sites, so this wasn't a problem.
My current job is at a very large manufacturing plant. Because of this, we must all observe a very strict dress code for security purposes. We can only wear pants (what ever type we want), no skirts or dresses. We must also always wear flat, closed-toe shoes - no high heels or sandals. Again, this is mostly done for the people who work on the production floor and, even though I never, ever go down there, I still have to adhere to the code. So, long story endless, my current work attire consists for jeans, sweater or t-shirt and Dr. Maartens