How am I only noticing this thread NOW?!
I'm so glad a lot of responses include console games, as that's where the bulk of my games-worth-replaying are. And thanks to emulators, I play them whenever I want. Though, let's be honest, it's not
quite the same as firing up the ol' NES/SNES/Genesis, am I right?
I'll keep my picks brief.
NES
Super Mario Bros. 1, 2 and 3
Legend of Zelda
Zelda II - The Adventure of Link (I'm doing yet another replay of this atm)
Metroid
TMNT II: The Arcade Game
Contra
Dr. Mario
SNES
Super Mario World
Super Metroid (and its various hacks. Some of 'em are amazing!)
Super Mario Kart
Super Mario RPG: Legend of The Seven Stars
Zombies Ate My Neighbors (one of Lucas Arts lesser-known games)
Donkey Kong Country 1&2 (Didn't care much for 3)
Super Empire Strikes Back (has a soft spot in my heart for being my introduction to SW games)
TMNT IV: Turtles in Time
Super Mario All-Stars
Super Mario World 2: Yoshi's Island
Earthworm Jim 1 & 2
Megaman X 1, 2 and 3
Genesis/32X/Sega CD
Sonic 1, 2, 3
Sonic & Knuckles (and the lock-on games)
Sonic Spinball
Star Wars 32X
Knuckles Chaotix
Sonic CD
Comix Zone
Dynamite Heady (which is still wacky to this day)
N64
Super Mario 64
Star Wars: Shadows of The Empire
Star Wars: Rogue Squadron
Legend of Zelda: Ocarina of Time/Master Quest
Legend of Zelda: Majora's Mask
Star Fox 64
PSX
Crash Bandicoot
Jet Moto 1 & 2
Megaman X 4, 5 and 6
Final Fantasy VIII
Street Fighter Alpha 3
Marvel Vs. Capcom (though the Dreamcast version is vastly superior)
Gamecube
Metroid Prime 1 & 2
Paper Mario: The Thousand Year Door
Super Mario Sunshine
Legend of Zelda: The Wind Waker
Legend of Zelda: Twilight Princess (prefer it over the Wii's mirrored version)
....and many others I'm probably forgetting
Also loved Metroid Prime 3 on the Wii, Tekken 5 on the PS2, GTA IV on PS3 (I'd really like to experience it on PC) and...that's about all I can think of at the moment. It's late and I'm tired