Contrary to popular belief, the Monopoly rules have not always been the same. There were some slight changes made to the "Chance" and "Community Chest" cards over the first decade of the games production. These changes may seem minor, but they are enough to substantially alter the statistics of the game. The main effects the changed cards had was to pump up the value of the railroads and utilities, while slightly reducing the value of the light blue properties.

Cards that were removed from the game
  • Go Back to Baltic Avenue
  • Parking Fine $15.00
  • Pay a $10.00 Fine or Take a "Chance"
  • Pay Your Insurance Premium $50.00
  • We're Off the Gold Standard Collect $50.00
Cards that were changed
  • Pay Poor Tax of $12.00 (changed to $15.00)
  • Pay School Tax of $150.00 (used to be a "Chance" card)
  • Second Prize in a Beauty Contest Collect $11.00 (changed to $15.00)
  • You are Assessed for Street Repairs (used to be a "Chance" card)
Cards that were added
  • Advance Token To Nearest Railroad
  • Advance Token To Nearest Utility
  • Collect $50 From Every Player
  • Pay Each Player $50

Other minor rules revisions included changing the rent on Marvin Gardens from $22 to $24, and changing the income tax square from $300 or 10 percent to $200 or 10 percent.

This writeup only applies to the American version of the game, as I don't believe any of the non-US versions came out until the rules were solidified.