The Committee of Crowd Control in Catalcysm (The CCCC)

In Cataclysm heroics, groups are tending to use Crowd Control as a means of making sure that the tanks, and therefore the group as a whole, do not get blown up by high damage.  However, lots of groups are unaware of which crowd controls exist and for which particular mobs, or that there is even a distinction.

So, first! There's a distinction! Mobs have a type; these types include:

Beast
Critter
Demon
Dragonkin
Elemental
Giant
Humanoid
Mechanical
Undead
Uncategorized

So it's important to notice that certain classes have no forms of crowd control for certain varieties of creature.  Hunters with their Freezing Trap are the only class that can deal with all forms of mobs, other than mobs that are purposefully immune to crowd control.  A detailed list, while out of date, is available here in case you are confused on what mobs can be dealt with by which classes.

One thing I do want to mention are the softer crowd controls.  These include snares, roots, stuns, silences, and cyclone.  They are not perfect crowd controls; they have positives and negatives associated with their usage.

The positives of these soft crowd controls is that they can be utilized to prevent damage to the tank or group.  Snaring or rooting a mob that is melee or has an "Explodes-at-melee-contact" mechanic is an excellent way of dealing preventing those targets from hitting any of the group members for a period of time.  Stuns, silences, and cyclones are great for caster mobs, particularly ones with long casts leading towards unhealthy amounts of damage.

The negatives of these crowd controls exist in that they are not permanent fixes to situations.  A stun or root will never fully replace sheep or fear as their durations are too short.  There are more negatives depending on which mechanic and ability is tied to it, so I won't go into detail here.  Just understand that these soft crowd controls can be useful where there's a lack of crowd control (Or more importantly, where crowd control has been broken).

I also just want to mention two crowd controls that are noticeably neglected, underused, or ignored.  Retribution Paladin's Repentance and Warlock's glyphed Fear.  There has long since been a stigma that retribution paladins are incapable of crowd control and that Repentance is only for PvP; however, this talent is mandatory in all Retribution specs and works just as effectively as Sheep (More effectively in that it actually covers more types of creatures).

There is also a misconception associated with Fear in that it will cause the mob to run away in fear and pull entire instances/heroics/raids and wipe the group with a single use.  With the new fear glyph, you sacrifice the spell's lack of cooldown in favor of stronger utility.