Makers of Crysis (Crytek), This is there first F2P game, with 4 Player coop, Free For All, and great team work modes.
http://www.warface.com/

Makers of Brink (Splash Damage) has a F2P Brink like shooter Don't know much about it.
http://extraction.nexon.net/

Valve's Source Engine made this game Contagion. Looks cool teamwork is a must in this zombie outbreak.
http://www.contagion-game.com/game/