I can't speak for them myself, because I haven't gotten mine yet, but the Enlightened Equipment Revelation X quilts come on high recommendation from everyone I talk to. I plan on using a 0 degree Rev X quilt with a warm pad combo in winter, but haven't tested it.
Zpacks (I hear) makes nice bags, and even lighter. However, they are roughly $100-$200 more expensive, in my opinion not worth it for a couple ounces saved.
I'll soon be getting my UL sleeping bags in the mail (Rev X for winter, Golite Adrenaline for summer), so I'll be able to speak from experience rather than other's recommendation.