What/Who is this Blue Dragon? And why is it in Orgimmar?
Though I'm not into WoW, it looks like somebody acquired the legendary staff Dragonwrath, Tarecgosa's Rest.
According to wowpedia:
Once the staff is completed, Blue Drakes will appear hovering above Stormwind and Orgrimmar.
These images both look similar, from mmochampion.org:
(source: mmo-champion.com)