Looking for some co-op PC games

[Dirty Hipsters]

One of my friends recently got a new PC and can finally play PC games. I introduced him to steam and he went absolutely nuts and has completely been converted to the PC master race (75% off sales tend to do that). My friend and I just finished Saints Row the Third, and we're playing Minecraft and we're looking for some other coop games to play.

List of games I already own and have recommended him (or which we have played):

Left 4 Dead 1 and 2
Portal 2
Torchlight 2
Saints Row the Third
Minecraft
Alien Swarm
Castle Crashers
Payday the Heist

Can you guys recommend me some good coop PC games that are not on this list?

 

[Dirty Hipsters]

So...nothing I guess.

 

[Orange12345]

Magicka
Orcs must die 2
Civ 5 (maybe?)
Awesomenauts
Terraria
Team fortress 2

Thats about all I got

 

[Auron]

Dead Island,Borderlands, Diablo and all it's peers.

Does this one count? http://store.steampowered.com/app/71165/?snr=1_7_7_151_150_1 Still an amazing game imho.

 

[oplinger]

so i made a list of my steam library of all games with a coop component to them. (not just multiplayer where you can be on the same team) so i'll just copy and paste that, some may be local coop too, so...yeah. Here you go.

Bionic Commando: Rearmed
Bulletstorm
Dungeon Defenders
Left 4 Dead
Left 4 Dead 2
Magicka
Neverwinter Nights 2
Portal 2
Serious Sam All
Civilization 5
Trine 2
Splinter Cell: Chaos Theory
Splinter Cell: Double Agent
Splinter Cell: Conviction
Alien Breed Series
ARMA 2
Borderlands
Commandos Series
Company Of Heroes: Tales of Valor
Dead Island
Dungeon Siege
Full Spectrum Warrior
Jamestown
Kane & Lynch 2
Orcs Must Die 2
Red Faction: Armageddon
Sacred
Saints Row 3
Steel Storm
Stronghold Legends
Titan Quest
Transformers: War for Cybertron
Trapped Dead
Unreal Tournament 3
Dawn Of War 2
Dead Horde
EYE Divine Cybermancy
Europa Universalis
GREED
Hoard

 

[Weaver]

Besides oplinger's list, there's also Castle Crashers but I'm not sure if it's online or local co-op (and I'm too lazy to check).

 

[saintdane05]

Army of Two is built around Co-Op, as well as all the Lego games and (Maybe) Republic Commandos.

 

[Elijin]

Im not going to repeat previously mentioned games (Those are some solid lists so far)

Im just going to add another name for consideration:

Killing Floor

 

[Stavros Dimou]

If you like visiting each other's house,get Serious Sam 3. It supports up to 4-player local split-screen co-op,but only 1 person can play with mouse and keyboard. The rest will have to plug in xbox360 controllers.
The co-op is a blast!

 

[Frezzato]

My friend and I just finished Saints Row the Third....

I thought co-op on Saints Row 3 was phenomenal. Co-op and single player were dovetailed so perfectly. I'm glad you played it with someone else because not many people do.