Darkmoon Dungeoneer

ADVICE1: As soon as you arrive on the DMF island, talk to the first guy you see on the LEFT in the camp and get the [item=71634] - You will ONLY be able to loot these quest items if you have [item=71634] in your bags.

The quest items seems to have a "decent" drop rate in ALL dungeons from one or two bosses in each instance. I would say that the drop rate is 33% - The drop is "static", so one boss will only drop a specific book no matter how often you kill it. Once you have completed the quest you can STILL loot the item again for selling on AH or trading to friends. But you can NOT turn it in again for additional tokens/rep until next DMF (next month).

ADVICE2: You can no longer farm low level dungeons. You now have to farm dungeons according to your own level for the items to drop. You might wanna "hardcore" farm heroics before everyone starts having the [item=71634] in their bags, once that happens everyone will be able to roll on them and it will be much harder to get (Everyone will want them for selling on AH).

Part of achievement:
Mysterious Grimoire from [npc=1853] in [zone=2057]
Mysterious Grimoire from [npc=7795] in [zone=1176]
Mysterious Grimoire from [npc=5710] in [zone=1477]
Mysterious Grimoire from [npc=6487] in [zone=796] - Library part
Monstrous Egg from [npc=10437] in [zone=2017]
Monstrous Egg from [npc=7273] in [zone=1176]
Monstrous Egg from [npc=26693] in [zone=1196] - Same boss who drop [item=44151] *hint*
Monstrous Egg from [npc=29120] in [zone=4277]
Monstrous Egg from [npc=3654] in [zone=718]
Monstrous Egg from [npc=31134] in [zone=4415]
Imbued Crystal from [npc=11520] in [zone=2437] - Orgrimmar (Horde)
Imbued Crystal from [npc=12201] in [zone=2100]
Imbued Crystal from [npc=10813] in [zone=2017]
Imbued Crystal from [npc=10508] in [zone=2057]
Imbued Crystal from [npc=26794] in [zone=4265]
Imbued Crystal from [npc=3977] in [zone=796] - Cathedral
Imbued Crystal from [npc=54853] in [zone=5788] - One of the new Heroics
Ornate Weapon from [npc=3975] in [zone=796]
Ornate Weapon from [npc=45412] in [zone=2017]
Ornate Weapon from [npc=47626] in [zone=1581]
Ornate Weapon from [npc=9568] in [zone=1583]
Ornate Weapon from [npc=46383] in [zone=717] - Stormwind (Alliance)
A Treatise on Strategy from [npc=40765] in [zone=5004] - Heroic
A Treatise on Strategy from [npc=4278] in [zone=209] - Heroic
A Treatise on Strategy from [npc=39378] in [zone=4945] - Heroic
A Treatise on Strategy from [npc=43214] in [zone=5088] - Heroic
A Treatise on Strategy from [npc=43878] in [zone=5035] - Heroic
A Treatise on Strategy from [npc=43875] in [zone=5035] - Heroic
A Treatise on Strategy from [npc=43612] in [zone=5396] - Heroic
A Treatise on Strategy from [npc=39625] in [zone=4950] - Heroic
A Treatise on Strategy from [npc=44577] in [zone=5396] - Heroic
A Treatise on Strategy from [npc=47626] in [zone=1581] - Heroic (Not confirmed)

Not part of this achievement but Darkmoon Despoiler and it is dropping from raid bosses only:
Soothsayer's Runes from [npc=53691] in [zone=5723]
Soothsayer's Runes from [npc=44600] in [zone=5334]
Soothsayer's Runes from [npc=41570] in [zone=5094]
Soothsayer's Runes from [npc=47120] in [zone=5600]
These can be looted by EVERYONE in the raid who have the [item=71634], not just one person !

If you find some drops that are NOT on my list, please reply below and I will add them. This will be helpful until the WoWhead looter addon starts picking up the drops later this week. And remember to vote if you found the info above useful.

Seems to be a "pattern", for those who wish to try find more drops:
Mysterious Grimoire = Humanoid caster bosses
Imbued Crystal = Non-human caster bosses
Monstrous Egg = Egg layer bosses - [npc=26693] might be a bit offended by this, but hey he is riding a dragon !
Ornate Weapon = Melee bosses
A Treatise on Strategy = Cataclysm heroic dungeon bosses who have army ranks

Collecting all the Darkmoon Faire Artifacts listed below will give you this achievement. The full list of Darkmoon Faire Artifacts and the quest related to it are:

1. 
   
2. Imbued Crystal & A Curious Crystal
3. 
   
4. Monstrous Egg & [quest=29448] / An Exotic Egg
5. 
   
6. Mysterious Grimoire & An Intriguing Grimoire / [quest=29449]
7. 
   
8. Ornate Weapon & A Wondrous Weapon / [quest=29450]
9. 
   
10. A Treatise on Strategy & The Master Strategist
11. 
    

To begin gathering the artifacts, Blizzard has stated (Source):

In addition, the [item=71634] can be obtained from [npc=10445], who resides in the first tent on your left as you enter the Darkmoon Faire ground on Darkmoon Island.

The Darkmoon Faire Field Guide

It’s your passport to riches, my friend. Y’see, we need a few things -- just some junk, nothing valuable to a big hero like you. We call ‘em Darkmoon Artifacts, and there’s all different kinds to be found all over Azeroth. The Darkmoon Field Guide helps you discover artifacts while you’re explorin’ dungeons, slayin’ monsters, and fightin’ in Battlegrounds. Without a guide, you’d never notice ‘em, and it’ll help keep you focused on the stuff we want. Whether you just reached level 10, or you’ve crushed the biggest baddies in the land, we need somethin’ from nearly everybody. You won’t have to go too far out of your way to get ‘em and each month you’ll get a new opportunity to seek out an Artifact for us. What do you get out of the deal? Don’t you worry, you’ll get your cut. When you bring a Darkmoon Artifact back to us, you’ll get valuable experience (it builds character, you know!), earn a better reputation, and possibly earn precious Darkmoon Faire Prize Tickets too!

Updated for mop and it looks like there are no drops in [zone=5918]. According to the wowhead, A Treatise on Strategy drops in heroic mode, and the other items drop in normal modes off the respective boss. I.e.: Ornate Weapon drops in normal and not heroic.

I've compiled a easy to see table of where each item for Darkmoon Dungeoneer can be found to get the most bang for your regular/heroic dungeon queues since Blizzard "fixed" the drops so that [faction=909] monthly quest items can only be looted in level appropriate dungeons. This is ordered in alphabetical order, with the instances that drops the most items for DMF items towards the top.

Notes:
I'm keeping the level 80 and 85 data for people who have not upgraded from the Battlechest and Cata to MoP.
If you find that a boss drops something not listed here. Leave a reply and I'll add it in, eventually.

Mists of Pandaria

Imbued Crystal

Monstrous Egg

Mysterious Grimoire

Ornate Weapon

A Treatise on Strategy

[zone=6182]

[npc=61398]

[npc=61398]

[zone=6052]

[npc=58632]

[npc=58632]

[zone=6109]

[npc=3977]

[npc=59223]

[npc=59223]

[zone=6066]

[npc=59080]

[npc=59080]

[zone=5963]

[npc=56717]

[npc=56717]

[zone=5956]

[npc=56439]

[npc=56439]

[zone=5976]

[npc=56636]

[zone=5918]

Cataclysm

Imbued Crystal

Monstrous Egg

Mysterious Grimoire

Ornate Weapon

A Treatise on Strategy

[zone=4945]

[npc=39732]

[npc=39425]

[npc=39378]

[zone=5844]

[npc=54938]

[npc=54968]

[npc=54938]

[zone=5396]

[npc=43614]

[npc=44577]

[npc=43612]

[zone=4926]

[npc=39698]

[npc=39705]

[zone=5789]

[npc=54432]

[npc=54432]

[zone=4950]

[npc=40177]

[npc=39625]

[zone=209]

[npc=46964]

[npc=4278]

[zone=5035]

[npc=43875]

[npc=43878]

[zone=5004]

[npc=40586]

[npc=40765]

[zone=5788]

[npc=54853]

[npc=54969]

[zone=1581]

[npc=47626]

[zone=5088]

[npc=43214]

Wrath of the Lich King

Imbued Crystal

Monstrous Egg

Mysterious Grimoire

Ornate Weapon

[zone=4494]

[npc=29310]

[npc=29308]

[zone=4196]

[npc=27483]

[npc=26631]

[zone=4265]

[npc=26794]

[npc=26723]

[zone=4277]

[npc=29120]

[zone=4416]

[npc=29306]

[zone=4272]

[npc=28923]

[zone=4264]

[npc=27975]

[zone=4813]

[npc=36658]

[zone=4100]

[npc=26530]

[zone=4415]

[npc=31134]

[zone=1196]

[npc=26693]