I absolutely love the song Sylvanas plays when you hand in the quest The Lady’s Necklace. The necklace in the quest used to belong to her sister, Alleria. If you are lucky enough to be the owner of Sylvanas’s music box you can hear this song all the time. However if you’re not, you can enter:
/script PlaySoundFile(“Sound\\Music\\GlueScreenMusic\\BCCredits_Lament_of_the_Highborne.mp3”)
into your chat box and it will play the Lament of the highborne song.