Silvermoon Robes

Source
This item drops from Fenissa the Assassin in Bloodmyst Isle. It is a vanity item, notable for its roleplaying value amongst the Blood Elf playerbase and as such, when sold in the neutral Auction House, commonly fetches high prices upwards of 30 gold. While it isn't as hard to farm as the Blood Elf Bandit Mask, it's nonetheless very hard to get when playing as Horde because of the location of the Bloodmyst Isle.