Ranking
There's a thread for this.

But anyway, Dragon's Nest is an action-MMORPG that I found quite good in its beta phase, and Spiral Knights is another which I found rather fun. Both are free-to-play action MMO's with microtransactions.
If you weren't looking for action MMO's (e.g. games which are all hotbars and clicking like WoW) then Guild Wars is an oldie but a goodie.