Most of you already encountered at least one rare spawn or maybe some hidden treasure around Pandaria.
The rare spawns reward you a random rare or if you are lucky a random epic item for you to wear, some bag of goods and gold. The same goes for the hidden treasures. There are a lot of them that reward you only gold or some expensive "trash" item and some of them give you wearable blue items.

In both cases, from rare spawns and hidden objects, you can get pets, vanity items and some special useful things. Let's see what actually you can find and where from.

Companion Pets
  Imbued Jade Fragment - dropped by Karr the Darkener, located in the Dread Wastes at (71,36)

  Hollow Reed - dropped by Nalash Verdantis, located in the Dread Wastes at (64,58)


Useful tools/items
  Ancient Pandaren Fishing Charm - you can get it from Ghostly Pandaren Fisherman NPC, located in the Valley of the Four Winds at (46,24)
This item is desired by every fisherman out there, so it will take you a while to catch that NPC to get it.

  Ancient Pandaren Mining Pick - you can get it from Ancient Pandaren Mining Pick object, located in The Jade Forest . It spawns in the Lower Quarry around (46,29)
Read the item's flavoured text. This is exactly what it does. If you have a miner, you should search for this pick.

  Forager's Gloves - dropped by Korda Torros, located in the Kun-Lai Summit around (50,83)
If you like to farm raw materials then this item is for you.

  Helpful Wikky's Whistle - dropped by Major Nanners, located in the Vale of Eternal Blossoms at (31,91).
You can summon a little monkey with this item and it will bring you a Bag of Helpful Things.

  Hardened Shell - dropped by Nessos the Oracle, located in the Kun-Lai Summit at (63,13).
You can use this item to dismount targets below level 94.

  Farwater Conch - dropped by Norlaxx the Outcast, located in the Kun-Lai Summit around (74,79).
If you want to use Far Sight and drop some water on the target then you should look for this item.

  Golden Fleece - dropped by Omnis Grinlok, located in the Dread Wastes around (39,61).
All the targets you kill have a small changes of dropping a pile of gold. You can loot about 10-30 gold.

  Aqua Jewel - dropped by Sahn Tidehunter, located in Vale of Eternal Blossoms at (62.55).
It gives you underwater breathing and 50% swimming speed.

  Salyin Battle Banner - dropped by Salyin Warscout, located in the Valley of the Four Winds around (71,52).
Similar to shadowmeld (more or less). You go out of combat and the mob you summoned will AoE taunt everything from you and from his path.

  Hozen Peace Pipe - dropped by Scritch, located in the Kun-Lai Summit around (46,61).
Thisi s a consumable item that reward you with 1000 reputation for some of the factions and only 100 reputation with others. See what factions are affected by it in the Reputation Calculator.

  Overgrown Lilypad - dropped by Sele'na, located in the Valley of the Four Winds around (55,31).
This item works like the druid Symbiosis ability.

  Crystal of Insanity - dropped by Sulik'shor, located in the Valley of the Four Winds at (37,25).
This is a neverending elixir.

  Tablet of Ren Yun - obtainable from Tablet of Ren Yun object, located in the Kun-Lai Summit at (44,52).
Cooking recipe.

  Recipe: Banana Infused Rum - obtainable from Barrel of Banana Infused Rum object, located in the Krasarang Wilds at (52,88).
Cooking recipe.


Items for your leveling alts
  Eternal Warrior's Sigil - dropped by Gar'lok, located in the Dread Wastes at around (35,30) within those Mantid buildings.
Basically if you are leaveling and you have this item you wont need food or drinks.

  Elixir of Ancient Knowledge - dropped by Krol the Blade located in the Dread Wastes around (74,22).
300% experience bonus while leveling before level 84. It's consumable and you lose the buff if you die.

How to get these items
You'll have to fly around a lot and camp a lot to get these items, especially on the high populated realms.
There are some nice tools to help you out and the one that you'll need it for sure is the NPC_Scan addon.
Most of the rare spawns are added and if you want to add something on your own you can do so, by adding the NPC id.
Just remember to clear the Cache as often as possible if you want this addon to be accurate.

Now, tell me if you already own any of these items and how hard was for you to get it? Also, what are you farming at the moment?