For me, the best one ever was "We love to fly and it shows!"

There could be no better service-oriented message, with a certain touch of exoticism.

"Delta is ready when you are" is still a valid business-oriented campaign (as well as the perfect retort to someone .....ing about something in Atlanta), but when you have good frontline people in the air, which Delta does (the whining by NW customers notwithstanding), that's a good slogan!

Now, if only there could be a slogan, "We love to get you on the flight in the seat you desired, and it shows!" that would be a killer.