I really hate to post this, but something has to be said about this game. This is probably THE best free games out there right now. It is almost the perfect armored warfare game I've played. I'm a fan of tanks and to be able to play as my favorite armored vehicles of yesteryear is one of my favorite things to do. It had me sold on these points.
Free: The game is free. You have the choice of buying gold which can buy special vehicles, shells with higher penetration, even special camouflage. This is not required, but it can improve gameplay.
No Hackers: Games like Combat Arms (another free game) is infested with hackers of various types. It is annoying and ruins the game. This game however, I have never encountered a hacker before.
Variety of vehicles: You have 4 nations each with roughly 30 vehicles (except for France which has about 18). Each tank has different modules, such as suspension (allows you to turn faster and equip heavier engines or guns), guns (which get more powerful, however a more powerful gun will fire slower), engines (which allow you to accelerate faster, or better going uphill) and turrets (which offer more protection, HP and turning speed). Making literally 1,000s of customizations.
Developers: These developers listen to their players as opposed to many free games (Combat Arms). They see problems that people face with video cards, sound drivers, even the vehicles themselves and fix it rather than ignoring it and assuming they have a strong enough community. Usually if enough people complain or request something it will happen.
This game is really good, but you have to try it for yourself to see if it fits your style. Hate to endorse a game that already has an add in the top, but I think it really is that good.