I just picked up a really sharp item. It's a Nike wind shirt with no-seem netting for venting, and it works most excellently. I pull it over my poly pro long sleave shirt in 30 degree weather, in the teens and 20s I pull on a light wool sweater in-between. It is pretty toasty. Of course I'm riding fixed gear with a messenger bag on my back, that's extra insulation. I've also switched socks to Smart Wool, and that's helped keep the little piggies warmer!