Suggest us some COOP games.

Jane's Advanced Strike Fighters, trine 2, beat hazard, the first templar, hoard, kane & lynch 2:dog days, warhammer 40k:space marine

portal2-sven coop :D or mario multiplayer :D

Natin Red,
Haunted - Hell's Reach,
Gears Of War,
Resident Evil 5,
RAGE,
Syndicate,
Raven Squad - Operation Hidden Dagger,
Close Combat - First To Figth,,
Rainbow Six 3 - Raven Shield,
Rainbow Six 3 - Athen Sword,
Rainbow Six 3 - Iron Wrath,
Rainbow Six Vegas 1 & 2,
Ghost Recon Advanced Warfighter 1 & 2,
Conflict - Vietnam,
Conflict - Global Terror/Global Storm (same game - different titles),
Conflict - Denied Ops,
Operation Flashpoint - Dragon Rising,
Operation Flashpoint - Red River,
Full Spectrum Warrior,
Full Spectrum Warrior - Ten Hammers,
SWAT 4,
SWAT 4 - The Stetchkov Syndicate,
Sniper Elite (PLAYSTATION 2),
Sniper Elite V2,
Hidden & Dangerous 2 - Sabre Squadron,
Splinter Cell - Chaos Theory,
Splinter Cell Double Agent (PLAYSTATION 2),
Splinter Cell - Conviction,
Kane and Lynch - Dead Men,
Kane and Lynch 2 - Dog Days,
Call Of Juarez - The Cartel,

Serious Sam, Saints Row games, get San Andreas and multiplayer mod it!

Try Black Ops or World at War. Coop Zombies (and coop campaign for the latter).

FPS/action-RPG: Borderlands (in summer Borderlands 2) if you have xbox you can play Border on splitscreen
RTS: Warhammer: Dawn of War II

If you can get through the many glitches, SWAT 4 looks awesome in coop.

wait for Orcs Must Die 2

Dungeon Defenders!

Pokemon :P

Punctuation.

Killing floor, Team fortress 2 ( Just need to find good server ;) )

Diablo 2! :D

Battlefield 2 yay!

rage.
warhammer 40.000 space marine have the coop mode "extermination". epic!!

Operation Flashpoint

KEYBOARD DRUMSET FUCKING WEREW... I mean LEGO series.

The ship is real fun and cheap!

terraria?

Half life 2

Portal 2, Synergy (HL2 Mod), Hawx, Dawn of War 2, Battlefield 3 Co-Op Missions ans Splinter Cell: Conviction.

Get Brutal Doom- a mod for the first two Dooms that makes it a blood orgy of awesomeness

Kane & Lynch / Portal 2 / Borderlands / Call of Juarez - The Cartel