While playing, press [CTRL] + [ALT] + [~] (tilde) to bring up the console, then type any of the following codes: 
 

Code:                              Result:
cmd(godmode)                 God Mode
cmd(noclip)                      No Clipping
cmd(giveall)                     All Weapons/Items
cmd(selfsummon)            Spawn Another Riddick
cmd(kill)                          Suicide
cmd(cyclecamera)            Switch 1st/3rd Person View