Spectral Wind Rider if you don't use the Shadowform Glyph. It looks very silly because you are sitting on nothing.
http://www.wowhead.com/item=76902#screenshots:id=292318
Hi Sephurik
Corrupted Fire Hawk, cause it's a big purple blob anyway.
Dark Phoenix ^ as above. Also shadowform makes it's body's shadow invisible, but not it's armor's shadow.
Frostbrood Vanquisher.
Fiery Warhorse, or Headless Horsemans Horse, or Crimson Deathcharger.
Ironbound Protodrake.
Red Flying Cloud.
Any Dragonhawk, just cause they have such a different profile from most mounts.
Tyrael's Charger.
Im using headless horsemans mount. looks pretty good tbh
I generally use my phosphorescent stone drake. Purple stones for a purple priest
i like the floating disc