I'm not really sure what a "commuter" is supposed to look like other than a guy or gal on a bike going somewhere. Apart from that...dress how you want and feel comfortable. Personally, I find jeans, regular shorts, etc extremely uncomfortable after 3 or 4 miles (actually I find them uncomfortable from the start but will deal with them for an under 5 mile trip). Past that, it is athletic wear, depending on what bike I am riding and where I am going. Unless I am being multimodal and riding in a car to my wife's office then taking a bike from there to mine, I am going to shower and change at work, so I might as well pull out the cycling kit and be comfortable. That's just me, though. Whatever you are comfortable riding in is what you should be wearing.