Drakes of the _____ Wind all look good as well as the Stone Drakes.
I think Ashes looks like ash in Shadowform.
Invincible is the best Spriest mount ever, hands down.
Spectral Wind Rider if you don't use the Shadowform Glyph. It looks very silly because you are sitting on nothing.
resto shaman <- Looking for Guild for 6.2
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.
Fiery Warhorse, or Headless Horsemans Horse, or Crimson Deathcharger.
Red Flying Cloud.
Any Dragonhawk, just cause they have such a different profile from most mounts.
I generally use my phosphorescent stone drake. Purple stones for a purple priest
i like the floating disc