I've been listening to "Caravan" a lot lately, and its importance as a piece is becoming more clear to me with each spin. Written by the trombonist Juan Tizol, and brought to its current fame by Duke Ellington, the tune may be the one that started two major schools in jazz. First, with its Latin and Mideastern melodies and rhythms, it is very likely the one that made jazz international. Second, with its long sections built on unstable chords (dimished and dominant), it may have been the origin of modal jazz (although the blues were involved as well, of course). And to top it off, it's just a great piece of music. Here's a terrific version: http://www.youtube.com/watch?v=z4XKHkzDggk.