There have been questions in the forums about libram and Zul Gurub enchants which should be answered by the information below. (Posted by Atkins)

ORDINARY LIBRAM ENCHANTS:

Libram quests require that a quest book (some drop in Dire Maul, others in various zones) be tendered at DM Library or the Horde flight point in Burning Steppes (will identify which place below) with certain materials and a fee of 30 gold. The NPC will give you an arcanum that you can later use to enchant a piece of head or leg armor in your inventory or through a trade window on another character's item. You can only have one of each type of libram or arcanum in your bank/inventory at one time, although you can have additional librams in the mail.

Any existing armor patches or enchants are replaced.

Constitution = +100 HP 
1 Black Diamond (BRD drop), 4 Night Dragon's Breath (from quest to use Cenarion Plant Salve to cure Corrupted Night Dragons), 1 Lung Juice (Blasted Lands repeatable quest reward). Turn in at Burning Steppes.  (All-round favorite, especially for melee and Warlocks.)

Focus = +8 Magic  (i.e., healing AND damage)
1 Pristine Black Diamond (drops in various instances, cheap on AH), 4 Large Brilliant Shards, 2 Skin of Shadow (Scholo).  DM turn in.
(Kind of a waste to use this on gear directly rather than as a component for ZG enchants.)

Protection = +1% Dodge
1 Pristine Black Diamond (cheap instance Drop), 2 Large Brilliant Shards, 1 Frayed Abomination Stitching (Strat).  DM turn in.
(Better than a Voracity AG boost, but the Libram is expensive now since in high demand for ZG enchants.)

Rapidity = 1% Haste (physical damage, so roughly 1% more DPS)
1 Pristine Black Diamond (cheap instance drop), 2 Large Brilliant Shard, 2 Blood of Heroes (EPL). DM turn in.

Resilience = +20% Fire Resistance
1 Black Diamond, 4 Crystal Spirit (10 yellow + 10 blue eastern pylon), 1 Burning Essence (BRD Dark Coffer BOP item).  Turn in at Burning Steppes.
(Expensive on AH due to high demand for raid instances.)

Rumination = +150 mana 
1 Black Diamond, 1 Gizzard Gum (Blasted Lands quest reward), 1 BLack Blood of the Tormented (BRD Dark Coffer BOP item). Turn in at Burning Steppes.
(Caster's special.  Note that this gives mana equivalent 10 untalented INT but not added crit chance or any other INT benefits.)

Tenacity = +125 armor 
1 BlackDiamond, 4 Crystal Ward (10 red + 10 green at Western Pylon), 1 Eye of Kajal (BRD Dark Coffer bop).  Turn in at Burning Steppes.
(Think of this as a pricey armor patch - does not multiply in bear form.)

Voracity = +8 STA (80 hp for most races and classes), 8 INT (120 mana), 8 STR, 8 AG, or 8 SPI
1 Black Diamond, 4 Crystal Force (10 greeen + 10 blue), 4 Whipper Root Tuber (from quest to use Cenarion Plant Salve to cure Corrupted Whipper Roots).  Turn in at Burning Steppes.
(These librams are cheaper than Constitution on AH for a little less HP, and are your only choice for misc stats.)

ZUL GURUB ENCHANTS

Zul Gurub class enchants are super-librams that use a libram of Focus, Protection, or Rapidity as a raw material and effectively give you benefits equivalent to three ordinary librams. These particular librams drop ONLY in Dire Maul.

Below is a list of all materials you need for the enchant.  What you need to turn in at a tower within Zul Gurub for the enchant itself (about half way through the instance) are Friendly faction, the BOP Primal Hakkari Item listed below, a class-specific BOE Punctured Voodoo Doll from ZG (available on the AH), and a completed Arcanum for the relevant libram from a turn in at the Dire Maul library (with lockpicking or the Crescent Key, you can avoid mobs and get to the library without combat).  Note that you can only have one of each of these items in your inventory at one time, though you can have more in the mail. 

Druid: Animist's Caress 

Permanently adds 10 Stamina, 10 Intellect, and increases healing by up to 24 to a leg or head slot item.
1x Primal Hakkari Binding
1x Punctured Voodoo Doll: Druid
1x Libram of PROTECTION
1x Frayed Abomination Stitching
2x Large Brilliant Shard
1x Pristine Black Diamond
(Good even for feral, though the Protection is costly now.)

Hunter: Falcon's Call
Permanently adds 24 Ranged Attack Power, 10 Stamina, and 1% Chance to Hit to a leg or head slot item.
1x Primal Hakkari Stanchion
1x Punctured Voodoo Doll: Hunter
1x Libram of RAPIDITY
2x Blood of Heroes
2x Large Brilliant Shard
1x Pristine Black Diamond
(Every hunter should get this, though the Rapidity libram is costly now.)

Mage: Presence of Sight
Permanently adds 18 to all healing and damage spells and 1% chance to hit with spells to a leg or head slot item.
1x Primal Hakkari Girdle
1x Punctured Voodoo Doll: Mage
1x Libram of FOCUS
2x Skin of Shadows
4x Large Brilliant Shard
1x Pristine Black Diamond
(Although Focus is cheaper than Protection or Rapidity, mages have grumbled that this is inferior to the enchants of other classses.)

Paladin: Syncretist's Sigil
Permanently adds 10 Stamina, 7 Defense, and increases healing by up to 24 to a leg or head slot item.
1x Primal Hakkari Shawl
1x Punctured Voodoo Doll: Paladin
1x Libram of PROTECTION
1x Frayed Abomination Stitching
2x Large Brilliant Shard
1x Pristine Black Diamond
(Good for all Paladins, although the Protection libram is costly now.)

Priest: Prophetic Aura 
Permanently adds 10 Stamina, 4 mana per 5 seconds, and increases healing by up to 24 to a leg or head slot item.
1x Primal Hakkari Tabard
1x Punctured Voodoo Doll: Priest
1x Libram of FOCUS
2x Skin of Shadow
4x Large Brilliant Shard
1x Pristine Black Diamond
(Perhaps the nicest class enchant, usable by every Priest.)

Rogue: Death's Embrace
Permanently adds 28 Attack Power and 1% Dodge to a leg or head slot item.
1x Primal Hakkari Kossack
1x Punctured Voodoo Doll: Rogue
1x Libram of RAPIDITY
2x Blood of Heroes
2x Large Brilliant Shard
1x Pristine Black Diamond
(Useful, but some rogues are put off by the price of the Rapidity libram.)

Shaman: Vodouisant's Vigilant Embrace
Permanently adds 15 Intellect and increases all healing and spell damage by up to 13 to a leg or head slot item.
1x Primal Hakkari Sash
1x Punctured Voodoo Doll: Shaman
1x Libram of FOCUS
2x Skin of Shadow
4x Large Brilliant Shard
1x Pristine Black Diamond
(This favors elemental and restoration Shamans, but is useful for all.)

Warlock: Hoodoo Hex
Permanently adds 10 Stamina and increases spell damage and healing by up to 18 to a leg or head slot item.
1x Primal Hakkari Armsplint
1x Punctured Voodoo Doll: Warlock
1x Libram of FOCUS
2x Skin of Shadow
4x Large Brilliant Shard
1x Pristine Black Diamond
(Exactly what Warlocks need.)

Warrior: Presence of Might
Permanently adds 10 Stamina, 7 Defense, and 15 Shield Block value to a leg or head slot item.
1x Primal Hakkari Aegis
1x Punctured Voodoo Doll: Warrior
1x Libram of PROTECTION
1x Frayed Abomination Stitching
2x Large Brilliant Shard
1x Pristine Black Diamond
(Clearly focused on tanking.  DPS Warriors may defer this due to the cost of the Protection libram.)