Xbox 360 fun co-op games?

[viralbug]

Hey guys!
Sadly I never get to visit this part of the forums since I don't own a console and miss out on a lot of great games. But I plan to buy a PS4/Xbox 720 when it launches.

Anyways, a good friend of mine bought an Xbox360 a few months ago. We need some good fun co-op games to play. So please suggest a few titles we should look to try out.

We've started with Halo:Reach and also have the GoW series to play.
(I also get to try my hands on RDR )

 

[Ethan_Hunt]

In no particular order:

Army of Two
Army of Two: The 40th Day
Gears of War series (goes without saying)
Scott Pilgrim V/S The World (XBLA)
Castle Crashers (XBLA)
The Dishwasher: Dead Samurai (XBLA)

 

[F3niX]

Gears of War is awesome for Co-Op.
You can also Play Portal 2

 

[dinjo]

Rayman Origins
50 Cent Blood on the Sand

 

[viralbug]

Thanks people.
Any good upcoming titles to look out for?

As I said, GoW series is obviously on the list. My friend said he'll be getting Portal 2 too.