The iron managed to stick around for a very long time (maybe because it had the lowest tendency to fall over). The patent issued to Parker Brothers on 12/31/35 lists the following tokens: iron, cannon, thimble, ship, shoe and top hat. According to a chart at the World of Monopoly, the iron was part of every Monopoly set since then except all editions from 1941-46 when tokens were made of wood or composites and the 2001 Nostalgia and Vintage editions.
I voted for the Robot, but unfortunately
In the battle to be Monopoly’s newest token, the Internet’s cat industrial complex crushes the real-estate hopes of robotkind. (read more at C|net)