Looking for fun game to play online?

I am looking for a game that you don't have to download persay, but something that I can play online with other live people. Something that is fun and most important FREE. Something where you can either earn ranks or levels. The sites that we can exclude as of right now is Pogo and myleague. Please give me some good ideas. Best idea gets 10 points. Again, game must be FREE. Thanks for your help guys!