Nethack is interesting, because it was tremendously popular inside a small group in its day, but obviously the population of people playing videogames was way smaller then compared to the millions of people playing things like GTA III and WoW now. That's also why I didn't mention Ultima IV, which absolutely dominated the market back then but, well, much smaller numbers compared to something like Quake.
Space Invaders I think gets an argument though, as does Breakout. People still play those games on phones and such.
I already had the Quake discussion in this thread, Red, pay attention. (Long story short - they put Doom in; I would either have put Wolfenstein in because it was first or Quake in because of its huge impact on gaming.)
Zork is also interesting, because although Infocom is now long gone you can still see its influence on the logic of adventure gaming.
Asterix the comic belongs in the Comic Book Hall of Fame, good god how many millions of books have they sold; however I'm not buying putting the videogame there.
Sonic the Hedgehog and Monkey Island, although I may in fact despise both of them almost as much as I hate Street Fighter, are also extremely influential. Ugh. Can I stop talking about them now?
Unreal Tournament & CounterStrike were both progressive evolutionary games from Quake II. Which, you know, isn't a bad thing; that could be said about pretty much all of our modern shooters, but eh.
Dune 2? Huh?
Civilization... same problem as the Elder Scrolls games. It sold well, and had a dedicated fanbase: but - not influential outside that group, and what's more it's basically a type of game that has completely disappeared now, so not a long-lived game either.
That said, SMAC is still one of my ten favourite games ever.