Western Mountaineering, Sequoia GWS, 6'-6" long, 36 oz of 850 down + 4 oz 'overfill', 4 lb-0 oz. WM conservatively rates this bag to 5F, but with the overfill it easily covers temps below zero F. I've had it 3 years and used it many nights in Alaska...always extremely warm and dry. At almost 3.5 to 4 lb (depending upon specifics) it's not a sheep hunter's bag most likely. The Sequoia GWS is a semi-rec bag and uses Gore Windstopper fabric. At this point in my life, I consider WM bags to be about the ultimate bag available on this planet.
I'll double the vote for the Marmot Helium only I suggest getting it with the waterproof Membrain shell. This bag is the BEST. I'm a bigger guy and it still offers a lot of room, is warm (15 degree) and still breaths well even with the waterproof shell. Plus it still is very lightweight. I also have the Marmot 30 degree Plasma for super ultra lightweight trips and I only rate this as fare. Not as much room as the helium and I think the 30 degree rating is pushing it.
Mountain Hardware Phantom 32 800 fill in Colorado until late season rifle hunts. It's light, packs to a nalgene stuff sack and you can combine with your choice down jacket to add what you need when you need too.