Good
South African Airways - Love the way the flag is portrayed on the tail.

Underappreciated
Finnair (old and current) - The tail logo is anF but looks like a plane. Cool.
Airtran (old) - Simple, clean, understated. Colors don't clash and the lines suggest movement.

Bad
Air Jamaica - Way too loud. It looks like a giant clown whose makeup has streaked from the high winds.