1) Bibs - I have a pair of uninsulated gortex bibs from Cabelas that I really like a lot. I layer with several different weights of capilene or polartec, depending on the temp and how much I plan to walk.
2) Balaclava - I bought an UnderArmor Balaclava last year, and I have to say, that it's the best $25 I've spent on cold weather gear. It totally seals out wind and cold air from your neck, which like your head, is a major source of heat loss.
3) Slow, shallow squats followed by a butt squeze (no joke!). For me, a set of 10 - 15 squats really gets the blood flowing if I'm on stand. Once I feel the shivers coming on I do a set and usually feel much more comfortable afterwards.