Austrian Airlines and Lufthansa seem to be offering the lowest prices to cities more in the Western Coast, where Austrian announced New York for 3050 NOK and Toronto from 3099 NOK. Meanwhile, Lufthansa has more less the same prices to the same destinations and to Montreal, but it also has offers around 3500 nok towards the middle of the United States and around 4000 nok towards the east.
The prices from both KLM and Airfrance are more around the 4000-4500-5000 NOK. But they have many more options, some for the south of the East Coast and a bargain of around 6000 nok to Hawaii! Considering that it is about 24 hours flying in order to reach Hawaii, I would say that the price is excellent =)
As almost all of those kind of promotions, there are a few conditions and you should do try several dates combinations to find the best price (a small cost for getting a nice discount). The conditions are:
Airfrance and KLM: Book before 06 December and depart between 07 January and 31 May 2012.
Lufthansa and Austrian Airlines: Book by 29 of November and take off between 09 January and 26 March 2012.
Have a nice trip!