Platinum-Iridium alloy is pretty fun too. The SI standard metre was made of it until they started defining it in terms of waves of light.Paradoxically, despite the high atomic weight, Uranium (with the density of 19,1 g/cm3) is not denser than Gold (19,3 g/cm3), or Platinum (21,1 g/cm3). However the most interesting is Iridium with the density of 22,4 g/cm3. Additionally (and surprisingly) Iridium is cheaper than Gold, not radioactive, and it is the most inert and stable metal of all metals known to mankind.