portal 2, borderlands, killing floor, l4d2,

the beta for "Dont Starve Together" is supposed to be pretty good

pretty much all of the recent splinter cell games

payday 2

system shock 2

Local co-op: Rayman Origins, Trine 1/2, Spelunky, Crypt of the NecroDancer
Remote co-op: Divinity: Original Sin, Orcs must die 2

FORCED is really fun, me and some of my team were just playing it. really intense.

(gameplay http://www.twitch.tv/withadancenumber/b/603935960)

we have to put more into it than we do tf2

sven co-op

anyone play far cry 3 coop? how was it?

worst ever far cry 3 no bad

Seconded, it's already had it's flash sale so wait until the last day to get it though.

Played a lot of it with some friends. It was pretty fun for a bit, but the missions are really linear and predictable (think L4D). I don't understand why they put tiny linear co-op missions as the only multiplayer feature in a sandbox game, but whatever.

Call of Duty WaW/Black Ops Zombies modes are always fun. There are tons of custom maps with a lot of cool features for WaW, but the game tends to not go on sale much.

Also Monaco, Risk of Rain, Hammerwatch, Killing Floor, Saints Row, Battleblock Theatre, Castle Crashers, and Nuclear Throne.

the new gauntlet is so fuckin terrible

borderlands is ok for a while. Other than that I've heard the Far Cry 4 Co-op is pretty good and the new don't starve beta is a lot of fun if that's what you're into

portal 2 is more fun than serious in case thats a factor you are looking for

Monaco ruined like 3 friendships of mine... still worth playing

Not exactly a co-op game but I recently completed the main story of Torchlight 2 with a friend and really enjoyed it.

Also recommend Portal 2, Sanctum 2, Saints Row, COD Zombies mods, and Synergy if you're into the Half-Life series.

distance
http://store.steampowered.com/app/233610/

My team plays a lot of Borderlands 1 & 2 (both are good, especially with the DLC), Far Cry 3 (sucks that they turn it into a linear shooter but it's still kinda fun), Payday 1 & 2 (I prefer the first by a solid margin, but both are great with friends), and Unturned (meh). I've heard good things about the Serious Sam's co-op modes.

Civ 5.

http://cloud-4.steampowered.com/ugc/536257828277189725/8833DCD54B1B235FAC0687D886D11ACBE3AFBE0B/

Just kidding

Another vote for sven-coop. Version 5 is coming up for steam and no dependency with HL1.

A lot of good games here, no one's mentioned Screencheat yet. It's hilarious.

Battlefield 3 had some pretty fun co-op missions.
Orcs Must Die! 2
Saints Row IV
Warframe
Doom 2
Magicka
Synery & Sven
Any of the Serious Sam games
Warhammer 40k Dawn of War 2

Serious Sam 3 yo

Payday

GTA4 (if you have controllers)

Dead Space or FEAR if you're into spooky

Orcs 2 is pretty good for a while, not a game I would play more than 3 times probably though

Magicka

Synergy mod, and Sven Co-op if you can find servers

Monaco

a lot of people liked Portal 2, although i personally didn't like it that much

Killing Floor. Alien Swarm would've been good if they updated it more, but it's pretty okay for one campaign.

Saints row 4, i think its also on sale right now

Lara Croft & the Guardian of Light

Magicka (must play)
Torchlight 2
Swat 4
Risk of Rain
Rayman Origins & Legends (must play)
Rainbow six vegas 2
Sniper Elite V2
E.Y.E: Divine Cybermancy (good bang for the buck, literally)
Dead Island
Borderlands
Left 4 Dead 1&2