I think we can all pretty well agree that the Helm of the Fire Festival, however practical it may be, is a fashion disaster.
The best fire-hats currently in the game are cloth and mail; I didn’t find any fire-hats that appealed to me in leather or plate. It’d say that this must be because the classes with Fire-themed damage specs — Fire Mage, Destruction Warlock, and Elemental Shaman — wear cloth and mail… but the first mail fire-hat has stats for a Hunter or Enhancement Shaman.
The cloth fire-hat is the classic Circle of Flame from Ambassador Flamelash in BRD. Many Transmogrification Template Kits have been created using this hat — but here are a few more.

Left: Mantle of Closed Doors (Normal), Corsair’s Overshirt (Normal), Archmage/Elementalist Belt, Spellstrike Pants, Soulcloth Gloves, Ritual Sandals
Right: Geomancer’s Spaulders, Corsair’s Overshirt, Sash of the Burning Heart, Crimson Silk Pantaloons, Ebony Flame Gloves, Embersilk Boots
The Soulcloth Gloves and Ebony Flame Gloves display under the sleeves of the Corsair’s Overshirt in MogIt. The display of these gloves in WMV is bugged rather badly, so the pictures show the Jumanza Grips and Embersilk Mitts — which display over the sleeves in MogIt as well.

Left: Exquisite Sunderseer Mantle, Cindercloth Vest, Grom’tor’s Bloodied Bandage, Crimson Silk Pantaloons, Earthmender’s Bracer of Shattering + Gloves of the High Magus, Infernoweave Boots
Right: Consortium Mantle, Flameheart Vest, Voidweave Cilice, Spellstrike Pants, Red Mageweave Gloves, Ritual Sandals

Arachnidian Spaulders, Corsair’s Overshirt, Wise Man’s Belt, Spellshock/Arachnidian Leggings, Soulcloth Gloves (not shown due to WMV bug), Outlander’s Boots (light brown shoes, invisible on this model)
The first mail fire-hat, the Crown of Destruction, drops from Ragnaros1.0 in Molten Core and is visually almost identical to the cloth Circle of Flame. The second mail fire-hat, the Crown of Flame, drops from Ragnaros2.0 in the Firelands. I prefer the Normal version to the Heroic version, and Kamalia will never, ever get rid of hers.

Left: Crown of Destruction with Bloodlust set
Center: Crown of Flame with Engraved set and Rocket-Chief Pauldrons
Right: Crown of Flame, Bloodforged shoulders, Bloodlust breastplate, Chiselbrand Girdle, Engraved leggings, Molten Fists, Radiant boots
I like the look of the Amber Filigreed Shirt underneath the Engraved Breastplate for the less-slender races.
Those trolls really accent a fire themed outfit so well, lovely against their blue skin!
They do, don’t they! The blue & orange is very Midsummer Fire Festival appropriate, too