1up has written an amazing piece, the essential 50 video games. Excellent catalog of the significant milestones in video game history. The individual game articles are well written, good combination of history and critique.
Video games are our culture's newest medium, as significant as the development of film. We're in the 1930 stage right now; a lot of the craft has been defined, but we're still trying to figure out the narrative form. But movies are easy to see, even eighty years later. By contrast video games require complex and idiosyncratic machines. I think only half of the games on this list are playable today unless you have the original hardware lying around.
Here, go play the original spacewar on a Java applet PDP-1 emulator. Brian actually typed in the code listing from a printout.
As seen on Joystiq