Leatrix Sounds is a complete sound kit browser for World of Warcraft. You can browse, search and play any sound kit in the game including emote sounds, boss sounds, NPC sounds, spell sounds, dialog, music, ambiance and more.
For example, you can search for things like Jaina, Muradin, Ymiron, Lich King, Power Word Shield, Gnome Female, Silly, Zone Forest Day, Forest Scary Night, etc.
Enter /lts to toggle Leatrix Sounds.
If you are looking for a sound file browser, check out Leatrix Tunes.