Crown of Kings +5

Increases the Strength, Intelligence, and Agility of the Hero by 5 when worn.

Source
Thrall can find one in The Oracle, chapter 7 of the Warcraft III orc campaign, The Invasion of Kalimdor.

Illidan can find one in The Brothers Stormrage, chapter 8 of the Frozen Throne sentinels campaign, Terror of the Tides.

Rexxar, Rokhan and Chen Stormstout can buy them in the store Orgrimmar Armory in the Bouns campaign, also they can find various Crowns through the campaign.

In the RPG
This impressive crown is made of gold decorated by lacy platinum strands woven delicately through the surface and around the borders. Gems and jewels of various types adorn the crown's twelve points; and in the center over the forehead, four huge emeralds surround a glowing black opal. Only a few of these impressive items are known to exist, all of them created for human kings in days long past.