So let us just assume you've got the greatest MMO game concept ever... ;)
Why not try to sell your idea to Blizzard? They are open for good ideas, and they are the best to market it. Of course, you would end up having Blizzard use your concept for their game, and maybe this is not what you want. On the other hand, consider them a competitor with your own game - maybe this is neither what you want. Think about getting an employment there.