Chapter III: Two Princes

One cup.

I wanna guess too!

Spin Doctors - Two Princes

http://www.youtube.com/watch?v=wsdy_rct6uo

The quests to complete this achievement stand like this:
Meet Me Upstairs
Secrets of the First Empire and I Need A Champion
The Thunder Forge-requires your realm to advance to the fourth stage on the Isle of Thunder, unlocked the Thunder Forges, and you to have completed To the Skies!. You meet him as a dragon by the Forge, and begin a tough, single-player scenario.
Spirit of the Storm Lord-you unlock the whole island and The Fall of Shan Bu to complete this, as that is when Nalak appears on Lei Shen's doorstep.
The Crown of Heaven-rewards a choice of 4 legendary meta gems:
[item=95346]
[item=95345]
[item=95344]
[item=95347]
Echoes of the Titans-Note: Titan Runestone can also drop from Ra-den's Cache of Storms and is also due to always drop from Lei Shen.
Heart of the Thunder King-achievement credit for Chapter III.
Note: All items drop in LFR and Normal (both 10 and 25-player).

A Reckoning-the lead-on quest that will continue in 5.3, although the patch will not have a raid tier-see here for more details:
http://us.battle.net/wow/en/forum/topic/7592242035#1
(Audio files suggest a cloak reward may be up for grabs!)

Edit: [item=87208], [item=87209], [item=94593] and [item=94594] will be able to drop from the first 9 bosses of the Siege of Orgrimmar (Immerseus up to and including General Nazgrim) for those that have the respective quests that allow the items to drop.
Source: http://blue.mmo-champion.com/topic/265970-54-ptr-patch-notes-august-7/