My favorite long johns are now all wool...Smart Wool being my top pick. These come in a couple of different thicknesses. I have a thin and a medium weight set and would not trade them for anything. I have mostly abandoned all my plastic underwear in favor of Smart wool.

This is a great time of year to be looking for these too, some retailers will begin blowing them out at good prices. These are not cheap but well worth the asking prices and if you can get a 30-50% deal this time of year they are very good prices.

Patagonia has recently introduced wool versions that I have not tried, but look good.

I have also used Ice Breaker, Ibex, Devold, and Filson wool long johns. Smart wool is still my favorite but the Devold in a terry knit is excellent for real cold weather. Filson is pretty scratchy and Ibex I do not like, Ice Breaker is a bit harder finished than Smart Wool but is good choice.

I also use Brynje poly string long johns but prefer these in milder weather or as a first layer then covered with the Smart wool. This combo was excellent for -14 deg in Montana last fall, but would be too much around here.

The best thing I have found with the wool long johns is that mositure management is vastly superior to poly garments. I never get the chilled feeling I get from plastic underwear.

Once I have the basic wool layer then I use wool shirts/sweaters (or fleece) and wool pants layered with windproofs and gaiters.