I've been using the military issue modular bag for awhile now, but without the thinner inner bag. I mostly got it for it's goretex bivy cover, but the synthetic bag is very decent too.
I'm very interested in the newer "waterproof" down, but haven't really researched it much yet.
I know Prima-Loft is very good too, have some snow pants made with it, but down just has a certain something. It just seems warmer, especially if you're trying to warm up, after getting chilled good.