Extreme Cold Gear (-20C and below). This keeps me comfortable on my daily commute for 1.5 hours. This setup is good for the -20 to -35 Celcius range, although with an extra layer on the legs and body you could extend into the -40s.
Head:
-Thin wind proof Earband, fleece on inside
-Face coverage from neckwarmer or ski type protector
-Ski/Snowboarding Helmet
-Ski Goggles
-Body:
-Wind proof shell
-Insulating layer cycling jacket
-Long sleeve jersey
-Regular jersey
Legs:
-Leg warmers
-Cycling tights, thicker ones if possible
-XC Skiing pants, part spandex mix with a mostly windproof outer
-Cycling shorts/bibs
Feet:
-Winter cycling boots
-Wind proof booties
-Battery powered insole warmers:
http://www.hotronic.com/ (I LOVE THESE!!)
-Two pairs of socks
Hands:
-Snowboarding gloves, thick insulated