Moreover, the sad fact is there are no synthetic-fill jackets that perform as well as a really good down parka. That's because synthetic fills are stiffer than down, hence mobility will suffer. Plus, a synthetic-fill jacket would of necessity be bulkier than its down equivalent. Still, there are some good pieces out there, provided you're not looking for one that will take you up Denali or to the South Pole. L.L. Bean, for instance, makes a fine all-around jacket filled with Primaloft, one of the more down-like synthetics. It's called the All-Conditions Primaloft Jacket ($149). Only thing is that availability is sort of erratic, and right now Bean is flat out of them -due in part, I think, to past recommendations by yours truly. Mountain Hardwear, meanwhile, makes a jacket called the Chugach that uses Polarguard 3D for insulation. It's $125. There's also a great buy out there, as REI has been blowing out Cerro Torre jackets from The North Face for $70, down from $160. It's similar to the Chugach.
Not sure this really solves the problem, though. All of these are pretty light pieces, best when worn under a shell. None has the flat-out warmth-per-ounce of down.