looks like Wargaming is going to have even more competition, even though it is covering different vehicles. Obsidian Entertainment (the guys behind Fallout: New Vegas for example) announced its new tank MMO, called Armored Warfare.
From its description, it seems to follow the basic World of Tanks pattern (battles of tanks with support tech, such as artillery), but it will focus on modern vehicles instead. On its official page, you can sign for beta as well. Apparently, the game will also have PVE content and will run on CryEngine.