A real estate site called Movoto.com just analyzed the current property values of the Atlantic City streets featured on the original Monopoly game board.  nd they found things have changed a LOT since the 1930s, when Monopoly was made.  First of all, Boardwalk isn't the most expensive property anymore, and Mediterranean Avenue isn't the cheapest.

A property on Boardwalk is now going for $669,000.  That's the second-most of any street in the game.  But the most expensive is MARVIN GARDENS, which is one of the yellow properties, at $1,175,000.

A property on Mediterranean Avenue is now $55,000.  That's actually more expensive than a property on Ventnor Avenue, which is also one of the yellows.  They're GIVING away property there now, at $22,000.

A few of the other streets from the game don't have properties at all, including Park Place, which is now just the entrance to Bally's Casino. 

(Movoto) 

Here's the Monopoly game board with prices from the game versus prices today.  You can see an enlarged version here.