All races will be playable by everyone in patch 5.0.4
In a stunning move, Blizzard has decided to make all races playable --including pandaren-- in the pre-expansion patch, while the pandaren will be available to all after launch. Even if you only have vanilla WoW or The Burning Crusade and even if you don't plan on getting Mists of Pandaria, you will be able to roll a character from any race.
Now, the only hard part will be choosing a name. Who will you be next?
The upper levels and their accompanying lands will still only be available to those with the appropriate expansions, of course. I think this will be especially good for new players, as well as those you bring in with the Scroll of Resurrection or Recruit-A-Friend.
Update: Pandaren won't be available until after Mists of Pandaria is released but will still be playable by anyone, regardless of latest expansion owned. Full clarification by Zarhym is after the break.
Just to be clear on the announcement, we're making it possible for people to create a character of any race, regardless of what expansions you've purchased. So if you only have the original game (which now has The Burning Crusade included), when patch 5.0.4 hits you'll be able to create goblin and worgen characters as well. And, once Mists of Pandaria is released, you'll be able to create pandaren characters, regardless of whether or not you own Mists of Pandaria.
Posted by Novagosa
So it says all races, what about though all classes? Just because Pandaren become available for play regardless if you have MoP or not, does this include the new monk class?
No, you'll need to upgrade your World of Warcraft license to Mists of Pandaria in order to unlock the monk class. The same is true for leveling from 85-90 and gaining access to the continent of Pandaria.
It's open warfare between Alliance and Horde in Mists of Pandaria, World of Warcraft's next expansion. Jump into five new levels with new talents and class mechanics, try the new monk class, and create a pandaren character to ally with either Horde or Alliance. Look for expansion basics in our Mists FAQ, or dig into our spring press event coverage for more details!