I like the Pearl-Izumi Amfibs if it gets below freezing, and Calientoes up to 45. For 45+ just a taped shoe vent is enough. Wet may change this though. Below 20 and I wear two pairs of cycling socks under the Amfibs.

At about 10 degrees and below, I wear thick black rubber galoshes with a cleat cutout. Man, that's one part of training in Colorado I don't miss