Some "Old world" advices :

Down:

Valandré, very very good, pricey : http://www.valandre.com/us/frontpage.htm

Warmth, less expensive, very good : http://www.warmthunlimited.com/


Synthetic:

Carinthia, military well known bags. some models with "central zip" : http://www.carinthia-bags.com/schlafsack/expeditionen/12.html

Helsport, good swedish brand, very compact synthetics bags : http://www.helsport.com/helsport/product...amp;pageid=5011