I have these. Good to about zero, or when it's wet out.
http://www.wiggle.com/sugoi-resistor-booties/
Last years model is 1/2 price at Bow cycle.
A friend of mine swears by these...
http://www.mec.ca/product/5028-496/d...isex/?q=defeat
http://www.mec.ca/product/5037-551/d...covers-unisex/
He gets them in Neon for the visibility.