Patagonia Nano Puff
The Nano Puff is one of the best jackets I've ever owned - love it. It's the perfect lightweight insulation piece and I wore mine a ton all winter long, practically lived in it - everywhere from chilly mornings in my basement office to traveling in Japan. It packs up super small into it's own pocket, so it's great to travel with, or to keep in the bc ski pack all the time as an emergency piece or to put on at the top of the hike.
The 60 grams of Primaloft is just enough to keep you warm, but it doesn't overheat once you start moving or if the temps warm up. The exterior shell does a good job of blocking wind and water, and is very comfortable as well. Can't say enough good things about this piece, and I'm looking forward to the cooler weather so I can start wearing it again