I was thinking about the rarest or most valuable (they don't always go hand and hand) games of each decade, and it got me thinking about what they could possibly be. Let's start a list, as I have never seen a similar topic. For now, let's focus on US official console releases first, then we can do foreign and computer games later.
1970's: No idea. Possibly something for the Fairchild Channel F, RCA Studio II, Bally Astrocade, or Odyssey II.
1980's: Stadium Events for the NES easily wins the most valuable, but it isn't the rarest. That distinction probably goes to Air Raid for the Atari 2600.
1990's: Nintendo World Championship 1990 Gold had to be the one.
2000's: I'm drawing a blank. Doesn't seem to be anything insanely valuable.
2010's: The decade is still brand new, just two months old. I'm guessing come March 16, the $100 God of War III Ultimate Edition will take the cake so far.