BA (old one indeed, strict and neat)
Quantas (kangaroo on the tail adds originality)
China Airlines (the flower looks so COOL)
Lufthansa (I like birds)
Aeroflot (I liked a USSR flag better than the new Russian)
I think those airlines that simply stick first two letters of their title on their tails should think of something more original and eye cathcing. I'm referring to American, British Midland, SAS, EuroScot...