My favorites are
1. Nagrand
2.Dun Morogh especially at night
3.Eversong Woods
4.Tol Barad
5. Old Tanaris / desert theme music
6. The song played when you die and in zones with undead, Duskwood/ Plaguelands/Tirisfal Galdes/ Silverpine Ect.
7.Vash Jir
8.Ironforge
9. Old Orgrimmar
10. Old Azsahra this music also played in zones like felwood and eastern plaguelands