Circlet of Nobility

Increases the Strength, Agility and Intelligence of the Hero by 2 when worn.

This ornamental piece of headgear is made of gold inlaid with platinum filigree. A single large emerald hangs down over the wearer's forehead, glowing slightly for as long as the circlet is worn. Legend has it these items were created for human nobles, but they have proven so popular that many adventurers now employ them.

Source
These can be bought from Goblin Merchants.

Thrall can find one in Cry of the Warsong, chapter 3 of the Warcraft III orc campaign, The Invasion of Kalimdor.

Tyrande can find one in Enemies at the Gate, chapter 1 of the night elf campaign, Eternity's End.

Malfurion, Tyrande, and Maiev can find one in Balancing the Scales, chapter 5 of the Frozen Throne sentinels campaign, Terror of the Tides.