I own the Enlightened Equipment Enigma (0 deg 900 fill) and love it for the weight/temp ratio...
I wish I could have gotten it at a Massdrop price, but at the $300 price it was a great deal compared to similar brands. I highly recommend this product.
For me, must be 850+ fill water resistant down, ultralight (sub 2Lbs 2 liters), and quilt style. 2 season (40 degree) would be OK, but 20 degree would be better. Zippers and sleeping Pad attachments, and around $300, better than SD Quilt 600 2S for $200 (REI)
Checkout the Kelty Tuck 20, I put it up to vote for. I am about to buy it at full price but if it's the perfect bag for others as well, might as well get it cheaper on here!
I have the enLIGHTENed Equipment Accomplice and Revelation. If I were to do it again, I would definitely pick the Enigma over the Revelation for a one-person bag because the footbox zipper on the Revelation can get a little annoying.
I have one of the Sierra Designs 3-Season Backcountry Beds, and it is fantastic. Took it to 20-degree temperatures for a week, and never got close to cold. I was definitely skeptical of the zipperless design, but I'm very happy with the results.