Though it isn't a FPS, you might be interested in the upcoming game Army of Two. I don't know a tremendous amount about it so I'll just quote Wikipedia:
'Army of Two (AO2 or Ao2) is a co-op third-person shooter with a focus on cooperative and coordinated strategies. Players will join up with either the game's built-in "Partner Artificial Intelligence" (PAI) or other players "to fight through war, political turmoil and a conspiracy so vast it threatens the entire world."
Co-op maneuvers
Expected multi-player maneuvers include:
Boost: One person stands up against a wall and holds his hands out while the other person gets lifted up. Second person can then reach down and pull first person up.
Rapelling: One person holds a rope while the other one scales down the side of a building or a large wall.
Back to Back: Both players go back to back to cover each other's non-armored backsides.
Makeshift cover: Players can tip over tables, and other objects to create cover. Players can also pick cover up and carry around with them. For example, car doors can be ripped off to provide a shield.
Death: Player that died will have to run away from "the light" while the other player goes through a button-mashing sequence to perform CPR.
Driving: All vehicles need one player to drive and the other to man the turret. Known vehicles are hovercraft, fork lift, jeep, buggie and a boat.
Ammo: If one player runs out of ammo, the other player can give him part or all of his magazine. Also players can trade guns at anytime.
Emotes: Both players can do a range of emotes from slapping each other to playing air guitar. Also characters will communicate a lot and talk trash to one another. For example when Salem was healing Rios, Rios said "Where did you learn first aid, butcher school?"
Healing: When one player is injured, the other player must run over to him and either drag him to a safe area or heal him in that spot.'