mostly, I wear either a polo shirt or simple oxford for casual wear...
Here in Florida, those polo shirts sold at Highland games with full-color embroidered clan badges are very popular.

These shirts are someone's inaccurate interpretation of 17th/18th C. shirts (they're usually called "Jacobite" shirts). They mostly resemble items from bad pirate movies! If you want a more authentic period shirt, here's an example:

http://www.ctraders.com/menshirts.html
True, but at $82.00 for a shirt I'll stick with my cotton Jacobites!