Petros

This list focuses on games in which you can play the entire single player game cooperatively, whether through mods or by default. Network co-op play is also must. Any additions or corrections you notice, let me know. I have not been able to verify a couple of these myself to ensure it's the actual single player campaign that is cooperative. I'm sure the mods in this list may become increasingly outdated as they die from time to time.
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Arma: Armed Assault
Armed Assault 2

Baldur's Gate
Baldur's Gate 2

Bionic Commando Rearmed

Borderlands

Brink

Call of Duty: World at War

Conflict: Denied Ops

Descent 3
Descent: Freespace

Diablo
Diablo 2
Diablo 3 (upcoming)

Dungeon Siege
Dungeon Siege 2

Doom
Doom II
Doom 3 Open Coop

Freelancer (Especially with the Discovery Freelancer Mod!)

Gears of War

Grand Theft Auto: San Andreas,
Vice City
GTA 3
San Andreas Mod Main Page

Half Life (via Sven Co-Op)
Half Life 2 (via Synergy Mod)

Heretic
Heretic II

Hidden and Dangerous
Hidden and Dangerous 2: Sabre Squadron

Icewind Dale
Icewind Dale 2

Left 4 Dead

Lego Batman
Lego Indiana Jones

Loki

Lord of the Rings: Conquest

Marvel: Ultimate Alliance

Mercenaries 2: World in Flames

Monster Madness

Neverwinter Nights
Neverwinter Nights 2/Mask of the Betrayer

No One Lives Forever 2

Operation Flashoint: Dragon Rising

Project Eden

Rainbow Six Games (Vegas, Vegas 2, GRAW, GRAW 2, just about any of them)

Rogue Warrior

Sacred II: Fallen Angel

Saints Row 2

Serious Sam
Serious Sam: The Second Encounter
Serious Sam II
Serious Sam HD

Silverfall

Space Siege

Splinter Cell Chaos Theory
Splinter Cell Double Agent

SWAT 4

System Shock 2 v2.3

Titan Quest
Titan Quest: Immortal Throne

Tom Clancy's HAWX

Trine

Typing of the Dead

World of Warcraft

X-Men Legends
X-Men Legends 2
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Useful Tools:
Logmein Hamachi (when a game allows only LAN play, this creates a virtual LAN over the internet)

Co-Op gameplay sites:
Co-Optimus.com

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ray_gillespie

Cool list man! There are never enough co-op PC games around. Don't forget the Serious Sam games, I know that at least the first two (First Encounter and Second Encounter) were completely co-op.

I'd love to play Far Cry co-op, that would be awesome. Pity my PC is the only one in the house that could run it!

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Petros

I forgot Second Encounter. Thanks!

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Bman

Yea a bunch of games co-op would be nice, yet I don't have more then 1 computer that can play games lol. Let alone anyone that would place with me lol

Nice list though.

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American Zombie

Sven Co-op and once you have that installed you can then also play Half Life cooperatively.

Petros

I didn't know that...wow thanks! Now I can play a game with people with older computers too I haven't used Sven Co-op since around 2000 so I imagine it's changed.

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SkyFuser

Would StarCraft count? Since it's basically same idea as World of WarCraft.
Although I must say, more and more people are illegally cheating at the Battle.net online multiplayer gaming. >_<

Lauzyguy

Starcraft should count you can team up with ur friends over LAN and battle it up with some ai players. It would also utilize cooperation through text, so I assume this would be considered a co-op game.

Also, Rainbow Six Vegas 2 came out a few weeks ago and there and it has a co-op story mode or terrorist hunt. You can also modify your characters now with different appearances.

Lauzyguy

Starcraft should count because you can play on BNet or over LAN with your friends. You would also be using teamwork against the opposing team. Also, Rainbow Six Vegas 2 came out a couple of weeks ago and it has a co-op campaign and a co-op terrorist hunt.

LocKStocK

Dont forget Synergy Mod for Half Life 2, that lets you play through the game with your mates.

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Petros

Updates made.

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