I have just started playing World of Tanks, and I am addicted. I think the game is brilliant, and I also find the fact that you can play against people on the other side of the world fucking mind blowing.
World of Tanks is free to play, but you can buy gold and use it to upgrade your tanks with armour and for buying tanks.
What other MMO's are there whether free to play or not, i heard there is a Star Wars one, what is that like.