On the cheap, I'm a massive fan of the poly/cotton standard issue military tee shirts. They dry fast, they're comfy, and they're non-descript. Lots of bike attire is fully synthetic and great for long ride comfort. But it tends to pill if you ride with a bag, and in my experience it also stinks more when the sweat dries on. The military tees cut back on pill and stink -- handy if you're stepping off the bike and into the real world. I've never tried wool, though ....