I personally would stick to cardies, sweaters, coats and scarves. Sweaters may or may not work, depending on fabric/design. Zippered ones as already mentioned, definitely. Crew neck, possibly. V-neck, not convinced personally. Buttoned shirts layer better over T-shirts than polos in my opinion.
A v-neck sweater would work. Also, I'd try making the polo shirt the outerpiece with a long sleeved shirt underneath the polo. Alternatively, the long sleeve shirt could be a buttonless henley and/or a long sleeved thermal shirt.
mrchapel- thanks i think i'm going to try that look
and for those of you who suggested v-neck sweaters, would i tuck in my polo as i would if i were wearing a button down underneath? do i keep my collar under the sweater or is it ok for the collar to be hanging out?
As you've seen from the responses above, there are a lot of possibilities for keeping up your polos during the cold weather. I have actually had good luck with sweaters and polos, although it looks best in my opinion if you wear a complementing sweater and polo.