In terms of raw nostalgia the first Final Fantasy on the NES does it for me. I remember it was the first game that introduced me to the RPG genre and already had the FF Prelude during the opening that I've come to love....it really takes me back. I can replay and enjoy it just because of nostalgia, I can tell, because if I analyze it coldly it's a very aged game with clunky mechanics. On the other hand, Final Fantasy VI is a game that relives the old days but also remains great by today's standards. I can't say it's childhood nostalgia because I was already in my teens when I played it, but it sure brings back great memories, I played that game to death several times. And its prelude is one of my favorites, every time I listen to it I get a warm magical feeling in my heart, it's just so beautiful. Not to mention the story is really powerful, I loved all the characters! I have lots of fond memories of this game, not only because it was a great fun game, but because it managed to ignite lots of strong feelings in me when I played. The good old days.

Sorted by time/platform:

Atari 2600: Asteroids, Pitfall, Space Invaders, Frogger
Atari 800XL: Pengo, Archon, Ice Climber, Panther, Alley Cat
NES: Super Mario Bros. 3, Donkey Kong, Rescue Rangers
SNES: Super Mario World, Zelda: A Link to the Past, Alien 3
Atari 7800: Centipede
Sega Megadrive 16-bit: Sonic, Ecco The Dolphin, Mickey Mouse and Donald Duck in World of Illusion, Ayrton Senna´s Super Monaco GP II
Amiga 500: The Secret of Monkey Island, Stunt Car Racer, Super Frog, Turrican 2, Agony, Galaga, Desert Strike, R-Type 2
Commodore Amiga CDTV: Out of this World, Reunion, The Secret of Monkey Island: Lechuck´s Revenge, Dragon´s Lair, Street Fighter 2, Golden Axe 2, Wing Commander 4 (in a 20GB DVD O_O!), Guy Spy, Lemmings, SWIV
PC: Indiana Jones and The Last Crusade, Indiana Jones and The Fate of Atlantis, Red Baron

Well, there might be others missing and some might have been released for multiple platforms, but, I sorted them according to the time and platform I played them in.

Probably Defender of the Crown and Hero's Quest: So You Want To Be a Hero

Definitely Commodore 64 titles. I'll just mention a few of them: Bruce Lee, , [url=http://www.lemon64.com/?game_id=1488]The Last Ninja, The Last Ninja 2 and The Last Ninja 3. I can easily add many more but since those games were first to come to my mind it apparently means that "they bring back the most nostalgia"

Eswat on the Sega Mega Drive

Games like Gorf and Pole Position are two that remind me of my late teens when we'd hang out in cafe's to play games and chase girls. Meanwhile, our college teachers were deciding whether or not they felt like turning up today.

Baldur's Gate is probably the biggest one for me. I (re)played that game more times than I care to admit and still love it. I like how cheesy and tongue-in-cheek it is, which are things I didn't really notice or realize 15 years ago. You can tell it was made by a bunch of D&D geeks who took a ton of ideas from their own pen and paper experiences and just put them in the game -- often with very randomly silly and entertaining results :)

Sure, BG2 is amazing and a massive accomplishment, but BG will always have a special place with me and, in my opinion, stands as a truer representation of what the spirit of D&D was all about at the time.