Treasure of Pandaria

A given character can only obtain each treasure once, as after you have received credit for looting a treasure, you are unable to see that treasure when it spawns again (barring changes to the system in 5.1 of course).

It is possible to track which treasures a character has credit for by querying the server as to the completion status of the "FLAG - (treasure name)" quests using the command '/run print(IsQuestFlaggedCompleted(xxxxx))', where xxxxx is the quest number of the associated FLAG quest.

I am reasonably certain that the treasures and quests line up as follows:

----------------------------Jade Forest-----------------------------

[item=85780] [quest=31400]
[object=214339] [quest=31864]
[item=85781] [quest=31401]
[object=214338] [quest=31865]
[item=86216] [quest=31404]
[object=213362] [quest=31396]
[object=214337] [quest=31866]

----------------------Valley of the Four Winds----------------------

[item=87524] [quest=31869]
[object=213650] [quest=31405]

----------------------------Veiled Stair----------------------------

[object=214325] [quest=31867]
[item=86473] [quest=31428]

--------------------------Krasarang Wilds---------------------------

[item=86220] [quest=31408]
[item=87798] [quest=31863]

---------------------------Kun-Lai Summit---------------------------

[item=86471] [quest=31420]
[object=213769] [quest=31414]
[object=213774] [quest=31418]
[object=214407] [quest=31868]
[item=86430] [quest=31419]
[item=86422] [quest=31416]
[object=213770] [quest=31415]
[item=86427] [quest=31422]

--------------------------Townlong Steppes--------------------------

[object=213961] [quest=31427]
[item=86472] [quest=31426]
[item=86516] [quest=31423]
[item=86517] [quest=31424]

----------------------(Other FLAGs with a non-obvious function) -----------------------
[object=214175] [quest=31466] This FLAG is a hidden daily which prevents players from looting the Wu Kao Supplies more than once per day.

------------------------------Unknown-------------------------------
[item=88669] [quest=31665] (This unavailable item and it's associated flag are likely unrelated to relics/treasures)

For a list of the Relic:FLAG associations, see here.

Edit: check out Paste (thanks oscarucb) for major assistance in getting all these lines pasted into WoW without the need of copy/pasting every damned line.

Coordinates & somewhat helpful info to go with Azurfel's list:

Jade Forest
/way The Jade Forest 26.2 32.4 Ancient Pandaren Tea Pot (100g grey item, on table)
/way The Jade Forest 24.0 53.0 Chest of Supplies (10g, bottom of waterfall near overturned boat)
/way The Jade Forest 31.9 27.8 Lucky Pandaren Coin (95g grey item, in fountain)
/way The Jade Forest 46.0 81.0 Offering of Rememberance (30g, on shrine)
/way The Jade Forest 23.5 35.0 Pandaren Ritual Stone (100g grey item, in between 5 stones on island)
/way The Jade Forest 51.0 100.0 Ship's Locker (96g, swim south)
/way The Jade Forest 62.4 27.5 Stash of Gems (green-quality gems & 6g)

Valley of the Four Winds
/way Valley of the Four Winds 43.5 37.4 Cache of Pilfered Goods (98g, underground)
/way Valley of the Four Winds 92.1 39.1 Boat-Building Instructions (10g grey item, inside boathouse on table)

The Veiled Stair
/way The Veiled Stair 75.1 76.4 The Hammer of Folly (100g grey item)
/way The Veiled Stair 68.1 79.0 The Hammer of Folly start path
/way The Veiled Stair 54.5 71.9 Forgotten Lockbox (10g, second floor of inn)

Krasarang
/way Valley of the Four Winds 75.1 55.1 Saurok Stone Tablet (100g grey item)
/way Krasarang Wilds 71.0 9.0 Saurok Stone Tablet entrance
/way Krasarang Wilds 52.0 73.0 Stack of Papers (15g grey item)

Kun-Lai
/way Kun-Lai Summit 64.2 45.1 Ancient Mogu Tablet (95g grey item, in room with Lost Souls)
/way Kun-Lai Summit 63.9 49.8 Ancient Mogu Tablet entrance
/way Kun-Lai Summit 49.0 59.0 Hozen Treasure Cache (gold only, next to 6 containers)
/way Kun-Lai Summit 36.7 79.7 Lost Adventurer's Belongings (gold only, inside tent)
/way Kun-Lai Summit 47.9 73.3 Mo-Mo's Treasure Chest (11g, small chest behind Mo-Mo)
/way Kun-Lai Summit 52.6 51.5 Rikkitik's Tick Remover (105g grey item + 50g)
/way Kun-Lai Summit 52.3 51.0 Rikkitik's Tick Remover entrance
/way Kun-Lai Summit 72.0 33.9 Statue of Xuen (100g grey item, at bottom of lake)
/way Kun-Lai Summit 56.7 48.9 Stolen Sprite Treasure (gold only, back of cave)
/way Kun-Lai Summit 59.0 50.0 Stolen Sprite Treasure entrance
/way Kun-Lai Summit 57.8 76.3 Terracotta Head (100g grey item, around this area, statue head on the ground)

Townlong Steppes
/way Townlong Steppes 62.8 34.1 Abandoned Crate of Goods (gold only, inside tent with 2 containers)
/way Townlong Steppes 65.8 86.1 Amber Encased Moth (105g grey item, to the right of the tree root)
/way Townlong Steppes 34.8 63.1 Fragment of Dread (90g grey item)
/way Townlong Steppes 32.8 61.6 Fragment of Dread entrance
No real way to point it out - Hardened Sap of Kri'vess (110g grey item; tiny orange blob found around Kri'vess)

Enjoy. I'll post this to the other parts as well.

There are two Treasure Hunt achievements in Mists of Pandaria - one sets you on a path to find 18 "Treasures", the other one requires you to find 20 "Lost treasures". When I started working on these achievements, I could not figure out the differences. But here they are:

Treasures (this one)
Achievements: Treasure of Pandaria, Fortune of Pandaria, Bounty of Pandaria and Riches of Pandaria.
These items are always there. Check Lilikoi's comment on Riches of Pandaria for the definitive list. The thing is that you can simply travel to all the specified locations, loot the items, and then you have found the 18 treasures and get the achievement. Simple and no fuss at all.

Lost Treasures (the other one)
Achievements: Lost and Found, Finders Keepers, One Man's Trash... and Is Another Man's Treasure
These items are rare spawns. There are many posts on the achievement pages describing what they are and where to find them - the lootable rewards you get are items (armor, weapons, etc) that are either Soulbound or Bind-to-Battle.net account. The thing is that these spawns are rare spawns. You can travel to the location, but more often than not, the item will not be there. You can camp a spot or you can travel around or you can get invited to other servers via real-id to check for them, but this is the tough one. For you achievement hunters out there, note that the last achievement requires you to find "only" 20 of these Lost Treasures - and there are (at least) 28 of them.

Some comments/pages will also - confusingly enough - mention items that does not count for the achievements - those posts are pre-patch 5.1. As they do not count for the achievement, you can safely ignore them. I think the reason is that before patch 5.1, there was a lot of confusing as to which items counted for the achievements, but after 5.1, it got a lot clearer. The posts, however, are still somewhat unclear and they at least managed to confuse me. I hope this post can help others, who are as confused as I was.

PS: Thanks to Salamizer, who finally was able to explain this to me :)