For me it would have to be a whole list of nostalgic games:

Heroes of Might and Magic 2&3 (1996/1999), Might and Magic 6, 7&8 (1998/1999/2000), Day of the Tentacle (1993), Indiana Jones and the Fate of Atlantis (1992), Age of Empires 1&2 (1997/1999), Master of Orion 1 (1993), Warcraft 2 (1995), StarCraft 1 (1998), Anno 1602 (1998), Command and Conquer: Red Alert 2 (2000), Empire Earth (2001), Gothic 1&2 (2001/2002), Indiana Jones and the Infernal Machine (1999), Little Big Adventure 2 (1997), Rayman 2: The Great Escape (1999), Oddworld: Abe's Exoddus (1998), Fantasy General (1996), Age of Wonders 1 (1999), Incubation: Battle Isle (1997), The Incredible Machine (1993)

I would be very surprised if there is anyone here who knows/has played all of them, some are fairly obscure, others not so much. Some of these are still among my favorite games to this day, others i have not even touched in a very long time. There are plenty of later games that i like more than some on this list but they just don't trigger the same nostalgia. I'm also not including games from this time period that i like but only discovered later such as Baldur's Gate.