Robe of the Magi +6



A Robe of the Magi +6 increases the Intelligence of the hero that wears it by 6.

Source
Furion can find one in Brothers in Blood, chapter 5 of the Warcraft III night elf campaign, Eternity's End.

Maiev can find this in The Broken Isles (WC3 NightElf), chapter 2 of the Frozen Throne sentinels campaign, Terror of the Tides.

Malfurion and Maiev can find one in The Ruins of Dalaran, chapter 7 of that campaign.

Illidan, Kael, Lady Vashj and Akama can find one in Lord of Outland, chapter 6 of the alliance campaign, Curse of the Blood Elves.