Belt of Giant Strength +6



A Belt of Giant Strength +6 increases the Strength of the hero that wears it by 6.

Source
Cairne Bloodhoof can find one in The Oracle, chapter 7 of the Warcraft III Horde campaign, The Invasion of Kalimdor.

Kael, Lady Vashj and Illidan can find one in Gates of the Abyss, chapter 5 of the Frozen Throne Alliance campaign, Curse of the Blood Elves.