I refused to participate in the Darkshore Warfront as Horde, but by participating in it as Alliance, I also gained the appearances for the Horde counterpart set.
Moonpriest’s Vestments (A), Plaguebringer’s Raiment (H)
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Moonpriest’s Vestments
Moonpriest
Moonpriest’s Vestments with Sentinel’s Branch/Crescent Wand + Urn of Lost Memories
Wrathful Moonpriest
Ceremonial Crown of Karabor, Wrathful Gladiator’s Silk Amice, Imbued Netherweave Tunic, Felcast Cord, Moonpriest’s Legwraps, Sunfrost Handwraps, Inferno Breath Sandals, Moonpriest’s Cloak, Steel Bladebreaker, Urn of Lost Memories
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Plaguebringer’s Raiment
Epic Wicked Witch
Wicked Witch’s Hat, Magnificent Aeroglide Shoulderpads, Plaguebringer’s Robe, Mana Cord of Deception, Plaguebringer’s Gloves, Pulverizing Felsoles, Ashjra’kamas, Shroud of Resolve (rank 1), Electrowing Dagger (H) + Ledger of Revolting Rituals (H)/Baleful Spire
Voidbringer
Mish’undare, Voidheart Mantle, Selis’ Silk Shirt, Mana-Cord of Deception (N), Plaguebringer’s Legwraps Gloves & Boots, Ashjra’kamas (rank 1), Inkgill Blade, Uldir Subject Manifest (LFR)
Kamalia et alia 
Part of me loves that there are thematic Alliance/Horde items. Part of me hates this because many times the “thematic” sets are anything but. So many times I needed an item that was the wrong faction to complete a mog set even though the set I needed it from wasn’t really thematic to factions.
Me, too! Sometimes I get annoyed because I want to put two items together, but one is Horde-exclusive and the other is Alliance-exclusive. For a lot of the Eastern Kingdoms and Kalimdor questing sets, you can get the same visual appearance of an item — sometimes with the same name, sometimes not — as both Alliance and Horde. I think that doing the Horde version of the quest will allow Alliance toons to use the Alliance version of the item without having done the Alliance version of the quest (and vice versa), though.