CS
WC3
SC:BW
Metal Arms: Glitch in the System
HoMM 3 if you count hotseat
Generals, Red Alert
Dawn of War 1/Dark Crusade/Soulstorm
Halo CE (and mods)
Borderlands 1
Diablo 2
Need for Speed Underground 2 (my fav), Most Wanted
Alien vs. Predator 2
Company of Heroes 1,2
Man of War (everything, especially with a infinite resources mod)
Dungeon Siege 1, 2
Doom 1, 2 (3 with coop mod)
Return to Castle Wolfenstein Coop Mod
Mass Effect 3 Multiplayer (private server hack, tons of fun and you can add millions of credits to yourself instantly)
Saints Row 2 (for 2 players)
Killing Floor 1 (2 if you all have legal copies but it's just not the same)
Quake 1, 2, 3, 4 (coop mod possible but I didn't get it running)
Sacred, Titan Quest, Grim Dawn, Path of Exile (not really),Torchlight 2
LoTR  Battle for middle Earth 2 (kinda dated and old), LoTR War in the North  (3players, lack of quality torrent last time I tried).
Stronghold HD/ Crusader HD, AoEmpires 2,3 AoMythology
CoD 1, 2, Modern Warfare 4, World @ War (have to fuck around with account creators)
Battlefield 1942, 2, 2142
Battlefront 1, 2
Baldur’s Gate 2, Icewind Dale 1,2 (but you need Infinity Engine mods such as high res patch and so on)
Minecraft, Terraria, Starbound (these are good for when a friend hosts a server and only you play, even if it isn't LAN it's nice)
Gauntlet (but it's more fun with 3 controllers + kbm) and Helldivers
M&B Warband and shitloads of mods
Serious Fucking Sam 1,2,3 (3 is hard to pirate)
Fucking Freelancer and those mods
Flatout 2
Gary’s Mod, Half Life 2 Deathmatch, EYE Divine Cybermancy
Jedi Outcast 2, Jedi Academy
Lego Games, Lego Star Wars, Lego LoTR, Lego Batman, etc.
Broforce
Castle Crashers
Worms, World Party, Armageddon, anything
Soldat
Crypt of the Necrodancer
Rampage Knights