The pilot of a Cessna 206 reported hearing an unusual noise as the nose wheel was lowered during the landing sequence. As a precaution, he increased back-pressure on the control column to keep the nose wheel off the ground for as long as possible during the landing roll. However, the nose wheel assembly subsequently collapsed, resulting in substantial damage to the propeller and engine cowling. An inspection of the failed nose gear assembly by a LAME revealed no pre-existing defect with the unit. This occurrence was not investigated by BASI. No reason was given for the failure of the landing gear.