Sometimes lyrics; the line from Wichita Lineman for example:
"And I need you more than want you, and I want you for all time"
This never fails to bring a tear; if lyrics were boxers, this lyric drops me to the canvas every time. The melody of the track is also instrumental in evoking this emotion.
Voices are also important to me. Some vocalists could sing the blurb from the back of a cereal box and evoke an emotional response; the late Mimi Parker of the band Low was one such artist