Before version 3.0 came out I was determined to get the Onyxia attunement since Blizzard was removing it and this was going to be the last chance to complete it.
The march through Stormwind ends with a reveal of Onyxia. This is easily the best quest line I have participated in since I began playing WoW.
Before completing the attunement you have to defeat a cave full of dragonkin, and two elite dragons. You can then teleport to meet Haleh where you receive the final stage of the quest.
Thanks to guildies Salemara, Starwinkle, and my friend Analar I was able to finish the very fun and exciting quest line.