I collect quite a lot of advertising posters including airline posters (
I have shown some in another thread)
I am on the look out for 2 Pan Am posters, one of which is listed on the site you linked to although the poor photo makes it look decidedly bland (one for London with bus).
I think TWA & Air France probably have the best airline posters, but there are some nice ones from other airlines. I wouldn't mind a nice Aeroflot poster if I can find one.
Mel, you should get into these kind of posters... the print quality is much better than for movie posters of the same vintage, often packing in strong colors. They can be rather pricey though...