In-jokes and references/items
Blizzard has included many in-jokes and pop-culture references in various forms throughout WoW.
Items
Angelista's items
Angelista is listed in the "Special Thanks" section of the WoW credits, and is most likely a friend or relative of a Blizzard staff member. She's had 5 items named after her: 
[Angelista's Charm], 
[Angelista's Grasp], 
[Angelista's Touch], 
[Angelista's Sash] and 
[Angelista's Revenge]. There is also a shop in Stratholme (that you can't enter) that used to belong to a person named Angelista, as you can read her name on the shield hanging atop the former entrance.
Blue Suede Shoes
The 
[Blue Suede Shoes] drop from Kaz'rogal in Hyjal, and are a reference to a song by Carl Perkins (famously covered by Elvis Presley). The yellow flavor text on the item says says "Keep Off", and the song says "don't step on my blue suede shoes".
Boomstick
The 
[Rough Boomstick], 
[Precisely Calibrated Boomstick], and 
[Lovingly Crafted Boomstick] are all probably references to the line in Army of Darkness: "Now listen up, you primitive screwheads. See this? This... is my boomstick! The 12-gauge double-barreled Remington". The 
[Sawed-Off Shotgun] may also be a reference to this.
Booterang
The 
[Booterang] is a reference to the 'Rifleman's Creed', a part of basic United States Marine Corps doctrine. The flavor text written in yellow is: "This is your booterang. There are many like it but this one is yours.". The first line of 'My Rifle' is "This is my rifle. There are many like it, but this one is mine. My rifle is my best friend. It is my life..."
Broken Barn Door
The shield 
[Broken Barn Door] and its flavor text, "It was open. How embarrassing," is likely a reference to the saying "Your barn door is open." The phrase is used to tell a person the zipper on their pants is down. A broken zipper may repeatedly fall down or be impossible to zip up.
Charlotte's Ivy and Lola's Eve (The Twin Stars)
The necklace 
[Charlotte's Ivy] could be seen as a reference to the book/movie Charlotte's Web. Together [Charlotte's Ivy] and 
[Lola's Eve] are seen as a (slightly odd) reference to the book 'Lolita' by Vladimir Nabokov. In the book, the main protagonist becomes obsessed with a young girl called Dolores (variously referred to in the novel as Dolores, Dolly, Lolita, Lola, Lo, L). The girl's mother is called Charlotte.
Crimson Steer Energy Drink
[Crimson Steer Energy Drink] is a reward from a quest in Zangarmarsh, Secrets of the Daggerfen for Alliance and Us or Them for Horde. It is an obvious reference to "Red Bull Energy Drink"
Dawn Treaders
[Dawn Treaders] are a possible reference to the C. S. Lewis novel "Voyage of the Dawn Treader".
Doctor in the House
The book 
[Master First Aid - Doctor in the House], required to learn 375 first aid skill, can be seen as a reference to "House M.D.", the famous TV series with Hugh Laurie. It is also likely that this is simply a reference to the phrase "Is there a doctor in the house?" used commonly in (vintage) film. "Doctor in the House" was a British television comedy series in the 1970s.
Empty Barrel & Hefty Barrel
You can sometimes receive an 
[Empty Barrel] as loot from the thunderers and stompers in the northeast of Un'Goro, which is a reference to Donkey Kong. This could also be a reference to "A barrel of monkeys.". This has been continued in Wrath of the Lich King with [Hefty Barrel]s dropping from Hardknuckle apes in Sholazar Basin.
Fight Club
There is a rare mace called 
[Fight Club], Presumably in reference to the Chuck Palahniuk book of the same name. Presumably, one does not talk about it.
Firefly
Several items are references the Firefly TV series, such as 
[An Antique Gun], 
[Mudder's Milk], 
[Broken Engine Part], and, of course, the 
[Captured Firefly].
Flintlocke's Piloting Pants
[Flintlocke's Piloting Pants] are a reference to the WoW comic "Flintlocke".
Jom Gabbar
[Jom Gabbar] is a "Dune" reference from the book of Frank Herbert, a Sci-Fi novel. It references to the "Gom Jabbar", which is a poisonous needle used by the Sisterhood to test the "humanity" of their students. It drops from the sandworm Ouro in TAQ
Lifelike Mechanical Toad
The 
[Lifelike Mechanical Toad] is a reference to Philip K. Dick’s Do Androids Dream of Electric Sheep. The novel is the basis for the movie "Blade Runner", but the toad is a reference to the novel, not the movie. In the novel, a lone android toad is discovered in a barren wasteland. And in WoW, you can learn how to make one.
Linken's Sword and Boomerang
The gnome, Linken, offers two rewards at the end of his rather long quest-line:
[Linken's Sword of Mastery]: In the Legend of Zelda games, it was common to take a weak or powerless sword and to travel all over the world in a quest to restore its power in order to defeat some evil power. The name is a reversal of the common name for Link's sword, "The Master Sword".
[Linken's Boomerang]: Another common feature is a boomerang, used to stun or disable enemies, or collect far away objects.
Malown's Slam
[Malown's Slam], a hammer which drops off Postmaster Malown in Stratholme, is a reference to former NBA star Karl "The Mailman" Malone.
Nigh-Invulnerability Belt
The 
[Nigh-Invulnerability Belt]'s name is a reference to the comic/cartoon/television character The Tick, who describes himself as "nigh-invulnerable".
Razor's Edge
[Razor's Edge]. Most likely a reference to the AC/DC album of the same name.
Red Riding Hood's Cloak
[Red Riding Hood's Cloak] is a reference to the famous fairytale Little Red Riding Hood. In the tale a wolf (often identified as the Big Bad Wolf) wants to eat the girl. Appropriately enough, this item drops from the Big Bad Wolf Opera Event in Karazhan.
Ruby Slippers
[Ruby Slippers] reference Dorothy's ruby slippers from the movie, The Wizard of Oz, which also had a hearthstone-like use: Dorothy was instructed to click her heels three times and say, "There's no place like home."
Rum Tum Tuber Surprise
[Runn Tum Tuber Surprise] is a reference to, The Rum Tum Tugger, one of the cats in T.S Eliot's Old Possum's Book of Practical Cats and the musical Cats.
Seaforium Charge
The Seaforium Charge is a type of item made by engineers that blows open locks. It is a reference to the C-4 plastic explosive.
Stung
[Stung] is a reward choice from the Anok'suten Horde quest, in the Ghostlands. It is a reference to Sting, the glowing sword used by Bilbo and Frodo Baggins. The spider lord Anok'suten is a hint at Shelob, the spider queen wounded by Sting.
Sulfuras
The legendary weapon 
[Sulfuras, Hand of Ragnaros] is seen as the ultimate sign of mastery of Molten Core (MC). Due to this hammer's connection to MC, it could be seen as a reference to MC Hammer.
Tenacious Defender
[Tenacious Defender] is an item from Hellfire Ramparts whose name clearly references the name of the band Tenacious D. The quote found on the item's flavor text is a reference to the song "Wonderboy".
The 1 Ring
[The 1 Ring] is clearly a reference to "The One Ring" from the Lord of the Rings books. "The One Ring" was discovered at the bottom of a river by Smeagol (later Gollum) and his cousin, Deagol, while fishing. [The 1 Ring] is a random low-level fishing drop. This ring also has its own joke: It's the 1 Ring, and it grants the wearer several +1 enhancements to their stats. The One Ring was the most powerful magical ring in Middle Earth, but The 1 Ring (while being pretty good for its level) is one of the lowest-powered rings in World of Warcraft.
It also appears that the popular pet site, Neopets, followed up on Blizzard's joke, and an item called "The Two Ring" is catchable from a fishing game. When moused-over, the tooltip states: "A slight upgrade." In patch 2.4, however, Blizzard actually implemented 
[The 2 Ring] as a reward from fishing daily quests.
The Arcanist's Cookbook
The Mage's book for the 
[Royal Seal of Eldre'Thalas] is named 
[The Arcanist's Cookbook]. This is a reference to The Anarchist Cookbook, the 1970 book that contained instructions on how to make bombs, among other topics.
The Don
There are a number of "Don" items in WoW. 
[Don Rigoberto's Lost Hat], 
[Don Julio's Band], etc.
The Emperor's New Cape
The final boss of Blackrock Depths, Emperor Dagran Thaurissan, drops 
[The Emperor's New Cape]. The name of the cape is a reference to a story by Hans Christian Andersen that tells of a vain and greedy emperor who is told that his new clothes can only be seen by the noble and worthy. Being vain and rather dense, he pretends that he can see the clothes. In a parade, a small child points out that the emperor is stark naked. In the end, the emperor realizes that clothes that are only visible to the worthy are, in fact, no clothes at all. The cape is also invisible. The cape may also be a reference to the cartoon, "The Emperor's New Groove".
The Light And How To Swing It
The Paladin book for the [Royal Seal of Eldre'Thalas] is named 
[The Light and How to Swing It]. A 1994 album by lounge singer Tom Jones is titled The Lead And How To Swing It. This title was probably inspired by the 1965 Richard Lester film, The Knack...and How to Get It.
Tusken Helm
[Tusken Helm] is a mail helm that drops from Overlord Ramtusk in Razorfen Kraul. It is apparently a reference to an item of the same name in the MMORPG, Star Wars Galaxies. The SWG version drops from (you guessed it) Tusken Raiders. It may also be a play on words, considering Razorfen Kraul is full of quilboars, who have tusks.
Unstoppable Force & Immovable Object
The mace 
[The Unstoppable Force] and the shield 
[The Immovable Object] are references to the pseudo-physics/philosophical question: "What would happen if an unstoppable force met an immovable object?" In The Burning Crusade, there is a gray mace from random drop, 
[The Stoppable Force]. Whether or not "The Movable Object" will appear remains to be seen.
Wirt's Third Leg
[Southsea Lamp] was a running inside reference between Blizzard games. Wirt's Leg was first found in Diablo II. Wirt's Other Leg was found in Warcraft III: The Frozen Throne. The fact that it is his "third" leg is becaus in diablo Wirt had lost a leg somehow, and had a wooden leg(see Wirt on the Diablo wiki). The term "third leg" is also likely a form of sexual innuendo.
Zandalarian Hero Charm/Medallion
There is a pair of trinkets called the 
[Zandalarian Hero Charm] and the [Zandalarian Hero Medallion], which is perhaps a reference to the Star Wars species Mandalorian, which are renowned as strong and fierce warriors and mercenaries with an immense capacity for self-healing. It just so happens that the charm trinket boosts your healing spells for a limited time, whilst the medallion trinket boosts your melee and ranged damage.
Staff of Prehistoria
The Staff of Prehistoria is used in Uldaman to unlock the boss Ironaya. To obtain the staff two items are needed, 
[Gni'kiv Medallion] and 
[The Shaft of Tsol]. When read backwards together these read LOST VIKING, a older Blizzard game.