These guys make a good bag.
http://www.sierradesigns.com/bags.mens.php
Just outta curiosity, whats wrong with the black and green bags along with the bivvy the Corps issues (or at least that was the system when I left in "04)?
They always kept me cozy while at Bridgeport doing cold weather training as well as in Norway. Are you looking for something lighter and more compact than the USMC issued bag(s)? FWIW, Snugpak makes a decent bag too.