Depends on the location and situation, but in the summer in the Sierra, where we normally hike, it's a pair of convertible hiking pants and a short-sleeved shirt. And sunscreen and a hat.
Normally running shorts of any name brand I find for cheap. I find running shorts dry faster. As it gets colder I'll add running tights(currently Under Armour I found on sale). I'll add rain pants on top of that for even cooler temps but am currently looking for a wind pants or something to put over.
Simple tee shirt of any brand(Academy normally has some decent stuff for cheap). I always carry one longsleave for sun, bugs, or extra warmth.