Slumberjack Big Timber -20°F
Source: bought it new
Price Paid: $79
Warm, roomy, comfortable and durable.
I can't say enough. I've been using the same Big Timber -20 since 2004 and spent several hundred nights in it. ...3 months in Alaska, 2005, and many horse pack trips high in the Sierra Nevada since.
I tend to be a cold sleeper. The bag never let me down. With a good air mattress I can look forward to toasty warm and restful nights high up in the cold freezing mountains. The bag does require a large commercial washer due to its size. It's been through the wash many times and just starting to show wear. I have a new one in reserve.
It is heavy and bulky, so no backpacking. Two make a good top load on a pack saddle.
Price Paid: $89
I bought this bag a couple of years ago to go Elk Hunting in Utah. It gets really cold at 8.000ft - 9000ft and we got snow. I climbed in my bag to try and get warm and after a few minutes I was just fine and I sleep in just my underwear.
I also do a lot of packing in on horseback and it works great for that as well. I would highly recommend it. If you want a big nice warm bag this is your guy.