Play Any Race In World Of Warcraft For Free
An upcoming patch for the game allows players to play as any race, regardless of which version or expansion packs you have.
Patch 5.0.4, among other things, lets you even play as the upcoming Pandaren when it is released on August 28. This is irrespective of whether you buy Mists of Pandaria when it comes out on September 25. Reading Blizzard's own blog entry on the matter, needless to say, it sounds like Pandaren won't be playable until the expansion hits.
Here are some more notes about the patch from Blizzard.
Also, be sure to check out Mists of Pandaria's epic opening cinematic.