I'm just going to go ahead and keep a new list here where I remember where it is. I'm going to go ahead and exchange the F2P tag with a PAID tag for Android games since most games on that platform are free.
3DS eShop/Virtual Console
Bloody Vampire [SP]
Earthworm Jim [DSiWare] [SP]
Fire Emblem: Awakening [SP]
Rune Factory 4 [SP]
Shin Megami Tensei: Devil Survivor Overclocked [SP]
Steel Diver: Sub Wars [SP + MP] [F2P]
The Legend of Zelda [NES] [SP]
The Legend of Zelda: Four Swords Anniversary [DSiWare] [SP + MP]
The Legend of Zelda: Oracle of Ages [GBC] [SP]
The Starship Damrey [SP]
Xbox 360
Assassin's Creed II [SP]
Crash Course 2 [F2P] [SP + MP]
Defense Grid [SP]
Happy Wars [F2P] [SP + MP]
Harm's Way [F2P] [SP + MP]
Halo: Combat Evolved [SP + MP]
Crackdown [SP + MP]
Ascend: Hand of Kul [MP]
Tom Clancy's Rainbow Six: Vegas [SP + MP]
Tales of Vesperia [SP + MP]
Hitman: Absolution [SP + MP]
The Walking Dead Season 2 [EP1]
The Wolf Among Us [EP1] [EP2]
Dead Island [SP + MP]
Sleeping Dogs [SP]
Deadlight [SP]
Dust: An Elysian Tale [SP]
Saints Row: The Third [SP]
Dark Souls [SP]
Battleblock Theater [SP + MP]
Dishonored [SP]
Steam
Agarest: Generations of War [SP]
Archeblade [MP] [F2P]
ARMA: Cold War Assault (Operation Flashpoint) [SP]
ARMA: Gold Edition [SP]
ARMA 2 [SP + MP]
Bastion [SP]
BioShock [SP]
BioShock 2 [SP + MP]
BioShock Infinite (+Burial At Sea 1+2) [SP]
BlazBlue: Calamity Trigger [SP + MP]
Cargo Commander [SP]
Cherry Tree High Comedy Club [SP]
Chivalry: Medieval Warfare (+Deadliest Warrior) [MP]
Cloudbuilt [SP]
Codename: Gordon [SP] [F2P, No Longer On Steam Store, Install via browser url steam://install/92]
Counter-Strike: Global Offensive [MP-Only]
Counter-Strike: Source [MP-Only]
Crysis [SP + MP]
Crysis: Warhead [SP]
Crysis Wars [MP]
Crysis 2: Maximum Edition [SP + MP]
Deus Ex: Human Revolution - Director's Cut [SP]
Dino D-Day [MP]
Dishonored: Game of the Year Edition [SP]
Dota 2 [MOBA]
Dragon Age: Origins Ultimate Edition [SP]
Elsword [MMO] [F2P]
Fallout: New Vegas Ultimate Edition [SP]
Far Cry 2: Fortune's Edition [SP + MP]
Half-Life [SP + MP]
Half-Life: Opposing Force [SP + MP]
Half-Life: Blue Shift [SP]
Half-Life Deathmatch: Source [MP-Only]
Half-Life 2 [SP]
Half-Life 2: Deathmatch [MP-Only]
Half-Life 2: Episode One [SP]
Half-Life 2: Episode Two [SP]
Half-Life 2: Lost Coast [SP]
Hydrophobia Prophecy [SP]
Garry's Mod [SP+MP]
GTR Evolution (+Race07) [SP + MP]
Gun Monkeys [SP + MP]
Insurgency: Modern Infantry Combat [MP-Only] [F2P, Requires Source Game]
Kung Fu Strike: The Warrior's Rise [SP + MP]
Left 4 Dead [MP-Only]
Left 4 Dead 2 [MP-Only]
Legendary [SP]
Mabinogi [MMO] [No Longer Play]
Microsoft Flight [SP]
MINERVA: Metastasis [SP] [F2P, Requires HL2: Episode One]
Mitsurugi Kamui Hikae [SP]
Metro 2033 [SP]
Metro: Last Light [SP]
Path of Exile [MMO]
Portal [SP]
Portal 2 [SP + MP]
Ragnarok Online 2 [MMO] [F2P]
Realm of the Mad God [MMO] [F2P]
Really Big Sky [SP]
Red Orchestra 2 [SP + MP]
ROSE Online [MMO] [No Longer Play]
Runespell: Overture [SP +MP]
Rusty Hearts [MMO] [SP + MP] [F2P]
Savant - Ascent [SP]
Singularity [SP + MP]
Spacechem [SP]
Spec Ops: The Line [SP + MP]
Super Crate Box [SP] [F2P]
Synergy [SP + MP] [F2P, Requires Source Games]
Team Fortress Classic [MP-Only]
Team Fortress 2 [MP-Only] [F2P]
The Elder Scrolls V: Skyrim [SP]
The Witcher: Enhanced Edition [SP]
The Witcher 2: Assassins of Kings [SP]
They Bleed Pixels [SP]
Tom Clancy's Ghost Recon: Phantoms [MP] [F2P]
Transistor [SP]
Vampire: The Masquerade - Bloodlines [SP]
Velvet Assassin [SP]
WiiWare/Wii VC
Cruis'n USA [N64] [SP + MP]
Donkey Kong Country 2: Diddy's Kong Quest [SNES] [SP + MP]
F-Zero X [N64] [SP + MP]
Fluidity [SP]
Kirby's Adventure [NES] [SP]
StarTropics [NES] [SP]
Super Mario Kart [SNES] [SP + MP]
Android
Russia's Army [MP-Only] [PAID]
Unlucky Hero [SP] [PAID]
Origin
Battlefield 3 [SP + MP]
Plants Vs. Zombies: Game Of The Year Edition [SP]
Sims 2 Ultimate [SP]
I'm not including pirated games on any of the platforms. (I don't even have any on Steam, Xbox, or Wii, just the Droid.) I included the MP-Only tag to MMOs because, though it seems redundant, some MMOs have campaigns that can be played through solo, which is different from Solo-ing a regular MMO. (Which is why Rusty Hearts has the SP + MP tag.) Not including any installed demos either. (Which I have a lot of on 360 and some of them still show up on my Steam library.)