Crowd Control

CC, or Crowd Control, is a term used to refer to skills that debuff or otherwise disable or distract enemies. While most CC skills do not deal direct damage, not all non-damage skills are CC; buffs such as some warcries and auras are not generally considered CC skills unless they have a debuff effect on enemies.

Most CC skills work differently against bosses and other players (in the Arena), with (at least) a reduced duration of effect compared to their function against regular monsters.

These types of abilities are not as common in Diablo III as in many RPGs, since all of the classes in D3 are designed to deal direct damage, rather than acting as support or healers. There are many more buffs than debuffs in Diablo III, as most classes have more ways to improve their own performance than to limit that of enemies. Most of Diablo III's CC skills are part of an attack that also deals damage.

Diablo III CC Skills

This list may be outdated by future game changes, and there is some debate about just how CC some skills are.

There will also be numerous runestone effects that change some of these skills from being CC to beign direct damage, and that change other skills to a CC-style effect.

All skills that deal cold damage can be considered CC, since chilled enemies move and attack at a slower rate. It's likely that numerous runestone effects will add cold damage, and it might be widely-accessible from equipment bonuses as well. It can also be argued that all minion skills are CC, since the minion or pet serves as a target for enemy attackers.

Barbarian Skills:
The Barbarian's CC skills are varied, with skills to knock back attackers with a couple of others meant to draw elusive enemies into melee range.

Ground Stomp -- Damages and stuns nearby enemies.
Ancient Spear -- A ranged attack that harpoons an enemy and drags them into melee range, while slowing their speed.
Seismic Slam -- Ranged attack that damages and knocks back enemies.
Taunt -- Enrages enemies, causing them to rush at the Barbarian while weakening their melee attacks.

Demon Hunter Skills:
Only a few Demon Hunter skills are yet known. It's certain the class has other CC abilities not yet revealed.

Entangling Shot -- Arrow attack that greatly slows enemy movement. May chain several nearby targets together.

Monk Skills:
The Monk has a wide variety of CC abilities that can knock back, slow, daze, drain, and otherwise afflict his enemies. Several of these come from his combo attacks, which can be mixed and matched together, potentially allowing the Monk to deal two or three different kinds of debuffs to the same target(s) in very rapid succession.

Lashing Tail Kick -- A roundhouse kick that damages and knocks back enemies.
Lethal Decoy -- Creates a duplicate of the Monk that attracts enemies before exploding and dealing Holy damage.
Blinding Flash -- A flash of liht that blinds all nearby enemies. Blinded enemies suffer a reduced chance to/hit and will not attack unless attacked first.
Crippling Wave -- This combo skill "dazes" enemies, reducing their movement speed.
Exploding Palm -- This combo skill creates a bleeding effect on enemies, dealing slow hit point loss and causing them to explode for huge damage if they die while the bleed effect is still active.
Retribution Aura -- Deals damage to all enemies in range, and causes their own damage to reflect back onto them. (Debatable if it's CC, since monster AI doesn't seem to be affected.)

Witch Doctor Skills:
The Witch Doctor has a few pure mind control skills, similar to the D2 Necromancer's curses, but only a few, since he is designed as a more active, directly attacking character.

Grasp of the Dead -- A curse that slows and damages enemies for several seconds.
Hex -- Hexed enemies are unable to perform offensive actions and take additional damage.
Horrify -- Frightens all enemies within range of the WD, causing them to run away.
Mass Confusion -- Incite paranoia in enemies, causing some to fight for the Witch Doctor for X seconds.
Minion Skills -- It's been suggested that any skills that create a target that monsters will attack, including pets like Mongrel, or Gargantuan, or even an obstacle like Wall of Zombies, should be considered Crowd Control skills, since they do modify enemy behavior. By that logic anything that draws enemies, including a merc or a follower, has a CC-type effect. There isn't a definitive yes/no answer to that issue, since it comes down to how one defines "crowd control"

Wizard Skills:
The Wizard's CC skills are mostly attacks as well. It's likely that many other Wizard skills will work like CC skills, if rune'd to deal cold damage.

Ice Armor -- Freezes and chills attackers, slowing their movement and attack speed.
Mirror Image -- Creates duplicates of the Wizard that move and attack for X seconds.
Wave of Force -- Knocks back enemies and incoming projectiles.
Frost Nova -- Freezes or chills enemies, slowing their movement/attack speed.
Ray of Frost -- A beam that chills enemies, slowing their movement/attack speed.
Slow Time -- Creates a protective bubble around the Wizard, within which all enemies and projectiles are greatly slowed.
Blizzard -- A powerful AoE attack that drops icy projectiles. Chilled enemies have their movement/attack speed reduced.

CC in WoW

CC skills are common in World of Warcraft and are used to debuff monsters and other players in PvP. They are essential to manage elements of WoW such as aggro. A quote from the WoW Wiki[1].

Crowd Control (abbreviated CC) refers to spells and abilities which limit an opponent's ability to fight. CC abilities are used to reduce the number of mobs that the group fight at once. Due to the fact that most groups cannot tank more than a certain number of elite mobs at a time, crowd control is often essential to prevent a group from being overwhelmed.

Reference

Crowd control (MMORPG) on Wikipedia
Crowd Control in WoW