I'll second the western mountaineering bags. I use to have a North face bag that was rated to 10 below zero and when it got down in the 20's (above zero) on a pad I was freezing my donkey off. Don't get me wrong it is a comfortable bag but when the temps dropped it is very lacking. After some long researching and talking with people out in the field I bought a Western Mountaineering Bristlecone Super MF. Man, I could not believe the difference, it's like comparing a neon to a Cadillac. Western Mountaineering rates there bags very conservatively, the rule of thumb is you can push there bags 10 degrees more than there rating. Yes, they are very expensive, but with a lifetime warranty and a killer reputation it was worth every cent. Definitely the last bag I would ever need. The one I got you can use as a blanket or a mummy bag, extra room for me inside plus cloths space at the feet. It's like an oven in it and has plenty of zippers to regulate the temps down to 10 below. There is no question I could easily take it to 20 below zero with some long johns and socks. It is by far the most comfortable bag I've ever had and I can unzip it and use it for a blanket for the misses on trips. These are as hardcore as you can get IMHO. Did I mention it is expensive and hot, but I looked as it as in my house I have a good mattress that I sleep on that helps on the back and makes me get a good night sleep, so I look at any out doors the same, I use it every where I go and put it in a watershed pack (http://www.drybags.com/home.html) and it's all but fireproof. All my bob and equipment is in watershed packs. They are rated at 300 feet of total water submersion and are currently used by Navy seals. My buddy who is a seal had recommended these bags. I ordered one and loved it then I started retrofitting my bob to be Katrina proof. The bag is black and has a purge valve on it and holds 6400 cubic in of space and has a backpack harness on it.
http://www.thewaterproofstore.com/paragonpack.html

http://www.drybags.com/home.html




http://www.westernmountaineering.com/ind...mp;ContentId=40