Mojos

"Witch doctors carry the aptly named mojos as spirit charms and vessels of good fortune. Many of them writhe in the witch doctors’ hands, or serve as symbolic representations of their enemies’ awful futures."

- Game Guide

Mojos are a type of off-hand item used only by Witch Doctors in Diablo III. They offer a slight increase in damage if used in lieu of a shield, and can also offer affixes specific to a Witch Doctor, such as an increase in Mana, or certain skill bonuses.

Mojos are often fashioned in form of grisly trophies, like the Necromancer's Shrunken Heads of Diablo II. These can be voodoo dolls, skulls, severed heads, otherworldly artifacts, or even living beings, like serpents. Through these, the Witch Doctor enhances his link with the Unformed Land and can hear the spirits more clearly. Many are nothing more than talismans (and images of the enemy's future for them to behold and tremble before), but some are artifacts of unspeakable capabilities, or even sentient monstrosities taking the form of a simple charm.

Diablo III
In addition to plain increase of damage (which is static, and therefore works better with fast weapons, does not count as an affix), all-armor and core stats, Mojo can also roll increased maximum Mana and Mana regeneration, Area Damage, Critical Hit Chance, a Socket, bonus damage against Elites, reduced cooldowns, increased damage of specific skills, reduced resource costs, increased Life and Life per second, extra healing, Thorns, and various 'chance on hit' effects. Legendary Mojos can also roll many other affixes.

Trivia

 * Mojo is an African-American word for any magical charm used in Hoodoo.