Nadine,
It would be easier to make suggestions if you could narrow things (ahem) down a bit on 3 fronts:
1) How warm is warm?
2) How weather proof do you want it?
3) Where is your personal value point?
In terms of warmth, I think you can roughly group the super warm parkas into 2 camps: a) expedition parkas that can go to Everest or Denali (ex Marmot 8000 Meter) and b) Belay parkas. Both of these styles have baffled construction like sleeping bags and almost always have attached hoods. The expedition parkas are going to be warmer, heavier, bulkier and more expensive.
In terms of weather and windproofness, the big question is whether or not you want a Gore type laminate in the shell to resists wind and moisture better. Good arguments on either side.
As is the case with sleeping bags, this is an area where the principle of diminishing returns kicks in. In general, you pay more for more thoughtful designs and marginal increases in durability and mariginal decreases in weight for a given warmth. Western Mountaineering and Feathered Friends will be top tier. Mountain Hardware and Marmot will be second tier. IMO, TNF, EMS and LL Bean (yes, Beans) will be roughly comparable.
Opinions differ but here's what I have.
I have a used Marmot (Primaloft Synthetic) Belay Parka with a plain Pertex outer. I don't regret having a non-Gtx type outer since it only gets used in dry cold (no rain). I do wish it was down for better compressability. I wouldn't bother with a full expedition parka because of weight and bulk.
I also have an EMS down sweater ($30 on clearance). I actually think the EMS design is better than the Marmot design in many ways I wouldn't hesitate with going with another EMS down jacket.