My favorites are
2.Dun Morogh especially at night
5. Old Tanaris / desert theme music
6. The song played when you die and in zones with undead, Duskwood/ Plaguelands/Tirisfal Galdes/ Silverpine Ect.
9. Old Orgrimmar
10. Old Azsahra this music also played in zones like felwood and eastern plaguelands