In an effort to preserve the history of videogames, a panel of developers including Warren Spector have elected the first ten games to be part of the IGDA's Digital Game Canon. Gamasutra has also started a series of in-depth articles examining closely those canon games (so far, they've covered Spacewar! and Zork -- the links are attached to the respective game below).
IGDA wiki page about the Digital Game Canon
Spacewar! (MIT, 1962)
Star Raiders (Atari, 1979)
Zork I: The Great Underground Empire (Infocom, 1980; PDP-11 version)
Tetris (Alexey Pajitnov, 1985)
Sim City (Maxis, 1989)
Super Mario Brothers 3 (Nintendo, 1990)
Civilization I/II (MicroProse, 1991-1996)
DOOM (id, 1993)
Sensible World of Soccer (Sensible, 1994)
Warcraft I/II/III (Blizzard, 1994-2003)