Alliance: Humans, Nightelves, Dwarves, Gnomes, Draenei, Worgen, Vrykul, Furbolgs.
Horde: Orcs, Tauren, Trolls, Goblins, Bloodelves, Forsaken, Ogres, Centaur.
Vrykul: For years the Vrykul viewed the Humans a a curse upon their bloodline. After recently seeing their King and God both slain by Human adversaries, The Vrykul have had a slight change in allegiance and pledge their loyalty to their descendants and assist them in destroying the Horde.
Furbolgs: Long ties with the Nightelves have already paved the way for the Furbolg's to join the Alliance. Now after the Draenei have also assisted them on Azuremyst and Bloodmyst, its as if they were destined to join the Alliance and defeat the Horde deforestors.
Ogres: Having heard glorious tales of the Horde's feats in both Outland and Northrend, the Ogres eagerly joined the Horde in hopes of establishing an alliance with them and helping them crush their Alliance enemies.
Centaur: Ever since the defeat of their Mother in Maraudon, the Centaur wandered Desolace aimlessly for years. Now with an offer of Peace and allegiance from Baine Bloodhoof, they readily accept the invitation into the Horde and now prepare themselves for the War against the meddlesome alliance.
What do you think? Also, Naga no because they serve the Old Gods. Pandaren No because we haven't hardly seen them in WoW. Murlocs/Gnolls no because that would be ridiculous.