Another vote for Spaceship Earth. My absolute favorite and the ride that kicks off a perfect trip!
Non-park, the bus ride back to POR after a long day. The darkness and quiet combined with the music and crickets playing gets me every time. I have to fight it to not be out like a light the instant it starts!

Do you have a favorite ride that gives you so much happiness that is has a calming effect on you? Other than WDW in general ;-) Which ride settles you the most?