what is the best ultra light weight warm...
what is the best ultra light weight warm (-20 degrees c) sleeping bag back packing?
It's not cheap but I think this is the best: http://www.backcountry.com/western-mountaineering-puma-super-mf-sleeping-bag-25-degree-down-wes0037
When it come to high quality sleeping bags, Marmot seems to always be rated at the top.
Check out the new Cal DriDown series from Sierra Designs. Super light and super warm.