Good coop/split screen/etc. games for PC?

Heroes of Might and Magic III

or
http://store.steampowered.com/tag/en/Local%20Multiplayer/
http://store.steampowered.com/tag/en/Split%20Screen/

Crawl is a great dungeon crawl/ asymmetrical multiplayer game.

trine, wwe, speedrunners, forced

Rayman Origins/Legends, Guacameele, Battleblock Theater, Castle Crashers.

Rampage Knights, Gauntlet

Lovers in a Dangerous Spacetime.

Renegade Ops is fun when it doesn't crash.

Brawlhalla (Platform Fighter)(F2P with no P2W, purely cosmetic).

• Can play offline vs, or online vs on the same computer.
• Only downfall is in game currency to buy characters can only be earned during online play and the 2nd player earns nothing extra for your account.

Sonic All-Stars Racing Transformed

Super Mega Baseball: Extra Innings

Meltdown (Arcade Shooter)

Contagion (FPS Zombie)

I would recommend:

Assault Android Cactus, Monsters & Monocles, Nuclear Throne & Enter The Gungeon (Great Co-Op twin stick shooters)

Also recommend Bears Cant Drift (IMO best Mario Kart style game on PC)

Porcunipine is also excellent.

Awesome games to play on the couch with friends :D :

Party saboteurs
Castle Crashers
Peggle
Lara Croft and the Guardian of Light (+ its sequal Temple of Osiris)
Halo: Spartan Assault
Pixeljunk Shooter
Sonic & All-Stars Racing Transformed
Speedrunners
Worms Blast

Towerfall Ascension and Broforce are godlike coop / versus games :)

Crimsonland, Triumph! War series, Guitar Hero series

Sonic & All-Stars Racing Transformed
Dungeon Defenders
Serious Sam
Need for Speed 3
Dirt Showdown
Dirt 3
Blur
SplitSecond
Proun
Burnout Paradise
Trine 1 and 2
Unreal Tournament 3
F1 2011

• Resident Evil 5
• Resident Evil 6
• Lara Croft and the Guardian of Light
• Kane & Lynch: Dead Men
• Gatling Gears
• Capsized
• Yars Revenge
• Atom Zombie Smasher
• Shadowgrounds Survivor
• Lara Croft and the Guardian of Light
• Kane & Lynch: Dead Men
• Worms
• Lego Batman
• Lego Star Wars 1 and 2
• Lego Star Wars III: The Clone Wars
• Lego Star Wars: The Complete Saga
• Lego Star Wars Clone Wars: Republic Heroes
• Lego Harry Potter
• Lego Indiana Jones: The Original Adventures
• Lego Indiana Jones 2: The Adventure Continue
• Magicka
• Nation Red
• Dungeon Defenders
• Sonic & SEGA All-Stars Racing
• Dirt 3
• Bionic Commando: Rearmed
• Split/Second
• Jamestown
• Civilization IV
• Civilization V
• GundeadliGne
• Audiosurf
• Beat Hazard
• NBA 2K12
• Blood Bowl: Legendary Edition
• Street Fighter IV
• Street Fighter X Tekken
• Trackmania
• Serious Sam 3 : BFE
• Renegade Ops
• Marvel Ultimate Alliance 1 and 2
• Rag Doll Kung Fu
• Football Manager 2012
• Rock of Ages
• Trine 2
• Worms Reloaded
• Worms Ultimate Mayhem
• Micro Machine 4
• Blue Toad Murder Files™: The Mysteries of Little Riddle
• Mortal Kombat 4
• Obscure 1 and 2
• Naval Warfare
• DeathSpank
• DeathSpank: Thongs of Virtue
• Shank
• Shank 2
• ProtoGalaxy
• Shrek Forever After
• Swarm Arena
• Magic: The Gathering
• Armada 2526
• Shatter
• Watchmen: The End is Nigh
• Gumboy Tournament
  Jamestown
  Dungeon Defenders
  Civilization IV
  Civilization V
  GundeadliGne
  Audiosurf
  Beat Hazard
  Worms Reloaded
  Worms Ultimate Mayhem

Terraria
Rocket League

You can play Divinity: Original Sin. A wonderful RPG.

BattleBlock: Theater and Castle Crashers

You can never hate Gauntlet, I love it
Also Diablo 3 is cool, I love the top down RPGs

One Piece: Pirate Warriors 3, or just the Dynasty Warriors games in general

The best ones so far:

GRID 2
Screencheat
Portal 2
Sonic & All-Stars Racing Transformed

There have been more and more couch multiplayer games popping up on steam over the past few years - the very best, in my opinion, are:

Local co-op:
Lovers in a Dangerous Spacetime - http://store.steampowered.com/app/252110
Chariot - http://store.steampowered.com/app/319450
Pitfall Planet - http://store.steampowered.com/app/464900
ibb & obb - http://store.steampowered.com/app/95400
Overcooked - http://store.steampowered.com/app/448510
Keep Talking and Nobody Explodes - http://store.steampowered.com/app/341800

Local Multiplayer:
BADBLOOD http://store.steampowered.com/app/404400
Duck Game http://store.steampowered.com/app/312530
Enter the Gungeon http://store.steampowered.com/app/311690
Rivals of Aether http://store.steampowered.com/app/383980
Ultimate Chicken Horse http://store.steampowered.com/app/386940
Push Me Pull You - http://store.steampowered.com/app/362380

Lethal League and Nidhogg are real nice couch fun.

Also Rocket Leeague and Castle Crashers.

I recently played Expendabros with a friend, good fun for 1 hour or so. (short free to play game)

They've been mentioned already I see but I think I'll add these as well...
Speedrunners
Worms
Trine
Battleblock Theater
Castle Crashers

The original Need for Speed III Hot Pursuit had a split screen modus that i used to play alot with my brother.
On the same keyboard :p
The game is ancient though

Serious Sam. But Mp community has now gone down. Was very active once.