Negatempest said:
Terraria and Minecraft both have local co-op on their console versions. Which is relevant because you're looking for couch co-op, so consoles totally count.
The Magic The Gathering games have local co-op in a 2v2 which you can do against the AI or online players.
Now here's a zero effort list, just going through my game library:
3on3 NHL Arcade: Little arcadey ice hockey game with teams of three, all 3 human player can be on one team, or spread across both, with AI filling the roles of unoccupied players. (Human players can switch to any AI body at will)
Battleblock Theater: Puzzle platformer with combat. Local co-op includes modified levels to encourage co-operation between the two players.
Castle Crashers: Skipping blurb, you're familiar.
Cloning Clyde: Puzzle Platformer with some wierd mutating mechanics.
Crimson Alliance: Top down hack and slash. Drops money (to both players) with a store inbetween levels for gear. So no loot quabbles.
Dungeon Defenders: You're familiar with this.
Earthworm Jim HD: The classic, in HD
Golden Axe: There's a few of these old ports in my list.
Warhammer 40K Kill Team: Fairly simple twin stick top down shooter.
Magic Games (4 of them): Already covered this. Each game adds new decks/cards.
Matt Hazard Blood Bath and Beyond: Sidescrolling 2D shooter.
Minecraft: Yep.
Monaco: Yep.
N+: Puzzle platformer, pretty chaotic, amusing fun even when you lose.
Phantom Breaker Battle Grounds: Sidescroller beat em up with some RPG mechanics. (Similar to Castle Crashers)
Scott Pilgrim vs The World: The Game: Sidescroller beat em up with lite rpg mechanics.
Shoot Many Robots: Sidescrolling 2D shooter.
South Park Lets Go Tower Defense Play! Tower defense game.
Spelunky: Roguelike exploration/platformer, Supports up to 4p local co-op.
Splosion Man: Puzzle Platformer
Streets of Rage 2: Heh.
Terraria: Yep.
The Dishwasher: Vampire Smile: Side scroller beat em up ninja game...thing.
TMNT Turtles in time: Heh.
That list is only even skimming through my arcade purchases (and Im cheap, the arcade is filled with local co-op goodies). People who say couch co-op is dead are either really badly misinformed, or just too lazy to go looking for what they want.
edit: This forum apparently does spoilers differently than Im used to.