If you wanna create a fantasy-themed MMO, which playable races do you put in?

Entirely depends on the world you're building and the scope of your game. The staples are, I suppose, humans, dwarves, orcs and elves.

Might be interesting to add some very inhumane species, like sentient plants, or plane-touched creatures (celestial, infernal, etc). I really loved in one game when I could play with a Groot-like tree creature. It could grow flowers instead of hair!