Here's a quick summary of the features and content that we're previewing for the World of Warcraft 4.3 patch:

PTR Patch 4.3 Official Notes: http://us.battle.net/wow/en/blog/3608419
The time for testing out many of the upcoming patch 4.3 features is upon us. In this article youll find frequent updates to the official patch 4.3 notes as development continues.

Balance Changes, Part One: http://us.battle.net/wow/en/blog/3615095
By popular demand for the explanation of patch 4.2 balance changes, lead systems designer Greg "Ghostcrawler" Street has returned to provide some context behind the intended upcoming patch 4.3 balance changes. Stay tuned for part two, as this information is subject to change over the course of the testing process.

Raid Finder: http://us.battle.net/wow/en/blog/3608426
We're also working on a number of other new features, including a Raid Finder -- a tool similar to the Dungeon Finder designed to match players looking for PUG-friendly raids.

Transmogrification: http://us.battle.net/wow/en/blog/3309048
The ethereals are setting up shop around Azeroth to offer adventurers their latest astonishing interdimensional service. The upcoming Transmogrification feature will let players customize the appearance of their gear like never before.

Void Storage: http://us.battle.net/wow/en/blog/3342240
Now that you've got a good reason to hang onto your old gear, you're going to need somewhere to store it all. With Transmogrification comes Void Storage, a long-term stash where players will be able to keep the items they just can't seem to let go of. Those ethereals think of everything, don't they?

Darkmoon Faire: http://us.battle.net/wow/en/blog/3390849
Its incredible! Its unbelievable! Youll be dazzled. Youll be amazed! You arent prepared for the Darkmoon Faire, cause its like nothing youve seen before! Dont be shy now, dont be bashful, step right up for a tantalizing glimpse of what weve got in store for you when patch 4.3 arrives!

Death to Deathwing
Alongside all this comes a whole lot of new content. We revealed at gamescom that patch 4.3 will feature three new 5-player dungeons, setting the stage for the ultimate fight in Cataclysm: the final showdown against Deathwing himself. Patch 4.3 will include a whole new tier of raid content culminating in an epic boss encounter unlike anything youve yet experienced in World of Warcraft.
End Time: http://us.battle.net/wow/en/blog/3502665
Well of Eternity: http://us.battle.net/wow/en/blog/3502666
Hour of Twilight: http://us.battle.net/wow/en/blog/3502667
Dragon Soul: http://us.battle.net/wow/en/blog/3516572
Legendary Preview: Fangs of the Father: http://us.battle.net/wow/en/blog/3579611
Valor Point Changes: http://us.battle.net/wow/en/blog/36151041

Tier 13: Of course you want to know how you'll look and what powers will be at your disposal as you give ol' Deathwing what-for.

Set Bonuses: http://us.battle.net/wow/en/forum/topic/3229376031

Art Design:
Death Knight: Coming soon.
Druid: http://us.battle.net/wow/en/blog/3469607
Hunter: http://us.battle.net/wow/en/blog/3676916
Mage: http://us.battle.net/wow/en/blog/3502705
Paladin: http://us.battle.net/wow/en/blog/3552221
Priest: http://us.battle.net/wow/en/blog/3615096
Rogue: http://us.battle.net/wow/en/blog/3516050
Shaman: http://us.battle.net/wow/en/blog/3502704
Warlock: http://us.battle.net/wow/en/blog/3469601
Warrior: http://us.battle.net/wow/en/blog/3435888
But don't worry -- there's plenty of time to prepare. Were keeping a close eye on players progress through the Rage of the Firelands content, and lots of folks are still busy working on obtaining the Dragonwrath legendary staff, completing the Molten Front dailies, and rallying to take down Ragnaros. Well have lots more details on the raid, dungeons, and other content coming in patch 4.3 in the months ahead, so keep an eye on the official World of Warcraft website.