Temple of the White Tiger

At the completion of this quest chain the gates to Vale of Eternal Blossoms will be opened which will gain you access to Shrine of Seven Stars which is the Alliance city hub in Pandaria.
(Or if you are Horde to Shrine of Two Moons.)

It has portals to Stormwind, Ironforge, Darnassus, Exodar, Shattrath and Dalaran.

It has bankers and auctioneer (for engineers only) and access to void storage, reforging and transmogrification.

And it has a flight trainer which on level 90 will teach you to fly in Pandaria.

Edit: Updated auctioneer info.

Head to 66, 58 for the path up to the Temple. The path is marked by tiny dots on the map, heading east off the road.

With the events of 5.4, this quest has been updated.

As you approach Xuen and co, the following exchange takes place.

Taran Zhu says: Half of the Vale lies in ruins! These outsiders have been more destructive than the mantid and mogu combined!
Anduin Wrynn says: Give us a chance to put things right.
Taran Zhu says: Great Tiger, the strangers from beyond the mists, they cannot be trusted. The wreckage in the Jade Forest can attest to this.

Turning in the quest to Anduin now reads as:

[class], I'm glad you're here! The "Vale of Eternal Blossoms" is legendary among the Pandaren. It's a place of great healing, if the locals are to be beleived. But the Horde Warchief has done something to the Vale - something terrible. We need to get in there!

The only line that changes during the battle is Anduin's line:

Anduin Wrynn says: We're here to lend our aid. We can help you rebuild the Vale.

Afterwards Xuen's decision changes to:

Xuen says: It is decided. The Vale of Eternal Blossoms shall remain open. The transgressions of the outsides have been great... but I see in them the capability to right what has been wronged.