Half-Life/Counter-Strike, Grim Fandango, Mario 64, Mario Kart 64, Ocarina of Time, Goldeneye, Turtles in Time, Ecco the Dolphin, Super Mario Kart, Sonic CD, Earthworm Jim, NBA Jam, Star Wars: Shadows of the Empire, Baseball 2020, Resident Evil 2, Tony Hawk, WCW v. NWO, Banjo Kazooie, Star Fox, Perfect Dark, Sonic Adventure, All-Star Baseball, Madden, etc.
So many. I loved co-op games. Back when there was no different types of co-op, it was just "local." Battle Toads Toejam & Earl General Chaos X-Men on Sega X-Men was my favorite. I never did beat that game. Always got stuck on that level with Mojo where he tells you to hold reset or something. Dammit I need to find it and beat the game.
NES River City Ransom Final Fantasy - the original Dragon Warrior II Wrestlemania Super Mario Bros 2 Mike Tyson's Punchout Sega Genesis Sonic Sonic 2 X-Men Spiderman Maximum Carnage (red cartridge FTW!) Altered Beast T2 Golden Axe NBA Jam TE NHL '96 Eternal Champions
PC Doom Diablo Starcraft Warcraft Genesis Sonic Golden Axe Streets of Rage Road Rash Playstation Bust A Groove Crash Bandicoot Banjo Kazooie Jumping Flash N64 Super Smash Bros Mario Party Mario Kart Golden Eye Honorable Mention: Gauntlet Legends
had a friend who was almost driven to tears by this scene. Also I have no idea why this part from FF3 always stuck with me. <iframe width="420" height="315" src="https://www.youtube.com/embed/hgZXiHfNt0M" frameborder="0" allowfullscreen></iframe>