"Though they are ornamental in appearance, only a fool would dismiss the amulet as decoration. Traditionally, they’re dangled from the neck and charged with mighty enchantments of defense and mastery – everything from warding off curses to prolonging the wearer’s life."
— Game Guide(src)
Amulets are talismans worn on the neck slot.
Amulets do not contribute to the overall look of your character in any way, and cannot be of normal quality; they may be only Magic, Set, Rare or Unique / Legendary. Amulets appear in all three Diablo games. In Diablo I and Diablo II, amulets are Indestructible.
Amulets can be Magic, Rare, Set or Unique Amulets.
Amulets may roll core stats, sockets, bonus damage, Area Damage, Attack Speed, Critical Hit Chance / Damage, Life %, Life per second, Life per Hit, Life per Kill, bonus healing, reduced status effect duration, reduced skill cooldowns, reduced skill resource costs, Armor, Thorns, resistances, bonus experience and Gold find. In addition, they can increase Elemental Damage of skills (i.e. Cold skills deal X% more damage, for example), and can roll chance to Blind on hit.
Legendary Gems can be socketed into Amulets.