Interesting question. I picked the last answer, but a more accurate response would have substituted cargo shorts for jeans. I bike to work everyday (6 miles, FL) in cargo shorts and a (cotton) t-shirt. I keep saying I'm going to use a running shirt, but I like to wear my biking shirt as an undershirt at work, and those look a little weirder. I don't sweat too much (except in the summer, when I might change my t-shirt) but it's flat and I go pretty slow. I keep all my work shirts / pants in my office.
I've also done a fair bit of bike touring, too. I never had cycling gear, but I do wear good travelling clothes -- quick dry stuff, mostly. I like those Columbia titanium button down shirts for sun protection -- I spent 30 days on the Tibetan Plateau, and the sun was extremely strong (but not overly hot) so I wanted long sleeves.
At the risk of revealing too much about myself, I wear boxer briefs, so I've never seen the point of spandex shorts. Am I missing something? And on my commuting bike, I use The Seat, which is pretty comfortable.