Taliesin238 - Act II isn't really the number one popcorn here in the USA - I am going to venture a guess that because it is cheaper than most of them and is also sold in Wal-mart which are EVERYWHERE here - they MAY and I am not at all sure about that - sell more than the other brands.
I think some of my families supermarket favorites (not the gourmet brands) are:
Orville Redenbacher
Jiffy Pop
Pop Secret
Maybe you can find a more definitive answer here:
http://www.popcorn.org/index.cfm
http://en.wikipedia.org/wiki/Category:Popcorn_ brands