Favorite Old School Arcade Game?

I realize that almost none of us were around for arcade's glory years, but I know that everyone has at least played many of the classics. So which of the old school namco/atari/snk/other games is your favorite? I'm really attached to the idea of owning an Neo Geo cabinet, but outside of that I'd have to say Galaga or Pac-Man is my favorite old school game.