I thought it was about time I uploaded some new inspiration. This is an outfit that I originally used for my priest - it is available for all cloth classes - but I think a fire mage would be able to lift this look to its full potential.
[Circle of Flame], Head
[Mantle of the Elven Kings], Shoulders
[Vermillion Robes of the Dominant], Chest
[Don Tayo's Inferno Mittens], Hands
[Sash of Serpentra], Waist
[Kavan's Foresaken Treads], Feet
[Staff of the Sunchaser], Staff (left), or
[Spire of Scarlet Pain], Staff (right)
As said, this transmog works for all cloth classes since it contains no class specific pieces. For a healing priest with main hand mace and an off-hand weapon, [Truncheon of Five Hells] (which hides enchants) together with [Darkmist Orb] are nice alternatives. This is a fairly easy set to obtain, so good luck!
EDIT: Also check out my newer, similar version of this set.