"I'm surprised I couldn't find a listing for the US military's Modular Sleep System (MSS), currently made by Tennier Industries. If you haven't seen them, you can find them on Ebay for info. Avoid the "mil-spec" ones--they're not the real deal and aren't nearly as good.
The MSS is similar to Wiggy's Flexible Temperature Range Sleep System (FTRSS), and consists of a lighter "patrol" bag (rated to 32 degrees F), an intermediate bag (rated to 0 degrees F), and a camouflage Goretex bivy cover (Wiggy doesn't seem to like Goretex, but I've had no problem with it as a bivy cover).
The newer ones have a the digital ACU pattern and sleeping bags of two shades of green. The older ones (up to 2005 or so) have the woodland camo and one of the bags is black. Other than that, the two versions are essentially the same.
It's a generously-sized mummy design, with a big footbox. I'm 6 feet, 175 pounds, with very broad shoulders, and I have room to spare in it.
When you use all three pieces, and wear the Army's ECWCS (longjohns, a grid fleece layer, and a thicker Polartec fleece layer), the Army says it's good down to -50F. (I'd add a cap too, I think!!) I haven't had it that cold yet, but might this winter and will report back on how it does in way-below-zero. One thing to consider--all military gear is tested, and ratings/specs are always straightforward and accurate. No wildly optimistic temperature ratings like most bags. If the Army labs in Natick, Massachusetts say a product does something, you know it does.
All 3 pieces snap together, so you can use one or both bags, with or without the cover. If the weather's not too cold, you can mate the patrol bag to the cover, and use the intermediate bag separately, to provide accommodations for two people.
Sometimes I use a CoolMax sleeping bag liner, which helps keep the inside clean and adds a few degrees of warmth.
It's synthetic laminar insulation (which I guess is something like Wiggy's Lamilite). Washable, and none of the problems of down.
And--hooray--like Wiggy's, it's also made in the USA. Almost everything else (e.g., TNF, Marmot, Mountain Hardwear, Walmart) seems to come from Communist China, the land of prison labor, horrid work environments, counterfeit products, and product safety recalls. I'm not rabid about it, but I avoid Chinese products whenever possible.
The verdict? I love my MSS. It's low-key (no screaming colors), American-made, does what it says and, best of all, it's warm warm warm. The only shortcoming I've found is that it's good to add a little Velcro to hold the top side of the bivy cover down and away from your face when you don't need complete coverage. Other than that, I have nothing but good things to say."