[Stance of the Wise Serpent] (Mistweaver specialization ability, level 10): Increases healing done by 20%, replaces your Energy resource with Mana, grants hit and expertise equal to 50% Spirit gained from items or effects, and increases haste received from items by 50%. Attack power is set equal to twice your spell power, and other sources of attack power no longer benefit you. In addition, you also gain [Eminence], causing you to heal the lowest health nearby target within 20 yards for an amount equal to 50% of non-auto attack damage you deal.
[Stance of the Sturdy Ox] (Brewmaster specialization ability, level 10): Reduces damage taken by 25%, increases Energy regeneration by 10%, reduces the chance to be critically hit by 6%, increases your stamina by 20% and allows you to [Stagger] damage.
Windwalker monks always used the Stance of the Fierce Tiger and couldn't switch stances. Mistweaver and Brewmaster monks had a choice between Fierce Tiger and their specialization-specific stance (Wise Serpent and Sturdy Ox, respectively). However, most of the time they would choose to remain in the specialization stances, as they are the ones optimized for healing and tanking, respectively.