What is a classic number from 'The Wizard of Oz'?

The beloved 1939 film version of 'The Wizard of Oz' is known for fine acting, choreography, costuming, set design, singing, and special effects. All of these elements and much more stand the test of time to make the movie one for all times, places and peoples. But perhaps the film's eternal appeal and cinematographic achievements best are epitomized in one classic, unforgettable number: 'Somewhere Over the Rainbow'.