PC:

Warcraft
Warcraft 2
Warcraft 3
Starcraft
Total Annihilation
Supreme Commander
Command & Conquer
Command & Conquer 2
Command & Conquer 3
Command & Conquer Red Alert
Command & Conquer Red Alert 2
Dune 2000
Emperor Battle for Dune

basically every RTS

TimeSplitters 3 had a better co-op mode then TimeSplitters 2!
Yet the multiplayer mode from TS2 was better then TS3:)

Armorines: Project S.W.A.R.M for the N64 had good co-op, too bad nothing else was good about it (according to professional reviewer standards). When I was younger, I think I actually enjoyed playing it though.

Contra is number one for me. I see it made your fantastic list. Good job!!!

PS3: Super Stardust HD

i Love Time splitters !

also i think the greatest Co op of this gen has to be Gears of war!

Baldur's Gate & Timesplitters 2 are on the GC also. And they are both awesome co-op games.

PS3 and 360

Army of 2 was great fun coop...single player sucked, but coop was great

I'd add the original Rainbow Six Vegas to the list.

Before i had online, me and my friends always played terrorist hunt/mission on co-op.

Little Ninja Bros for the NES was crazy fun. (And truly "Nintendo hard".)

Ikaruga for the Cube (and Live Arcade, I guess.)

The X-Men Legends games and Marvel: Ultimate Alliance were fun with a few friends.

FF:Crystal Chronicles for the Cube was a blast with 4 players and 4 GBAs. (As the only person in the world who owns an entire 4 player FF:CC setup by himself, I can vouch for the fun factor. Also, my insanity.)

Also, how have you forgotten the original Xbox's answer to Killzone in the "overhyped 'AAA' game that actually turned out very mediocre" contest: Brute Force. Some people apparently liked the co-op.

Also, I'd submit the Guitar Hero games and Rock Band for the PSWii60.

Of the ones already listed, my personal favorites woudl include the Timesplitters games, the old TMNT arcade games (Turtles in Time FTW), the first couple Double Dragon games, Battletoads, Contra, and Secret of Mana. Seiken Densetsu 3 needs to be localized for either the DS or Virtual Console, because that game is freaking amazing, and you can only play it in the US via emulator.