Michelle, you hit on the really good ones but here are a few more than always make me crack up! 

1.  Elaine: There's no reason to become alarmed, and we hope you'll enjoy the rest of your flight. By the way, is there anyone on board who knows how to fly a plane? 

2.  Ted Striker:  Mayday!  Mayday!
Steve McCroskey:  What the heck is that?
Johnny:  Why, that's the Russian New Year.  We can have a parade and serve hot hors d'oeuvres! 

3.  Captain Oveur: Joey, have you ever been in a... in a Turkish prison?