If there is one thing I love about WoW it is the sounds and affects. I could recognize any WoW sound and apply it to what it is doing in game, as I'm sure most long time players could. So, what is your favorite sound? It could be a spell cast, npc noise, level up, etc etc.
My personal favorite WoW sound is the sound when the Alliance take a flag or capture a node in a BG. I PvP a lot as Ally so it means that we are doing something right .