I was thinking about the value of souls.  I do like the idea of a tier system as opposed to a hit dice formula. It gives the DM better control.  For example,  names blatantly ripped from TES.<br/><br/>Petty Souls: 10 gp - These are things that are of animal intellect as well as weak monsters with out any kind if society or capacity to think beyond "eat,  sleep,  eat,  reproduce". These souls aren't usually traded for.<br/><br/>Lesser: 100 gp - Commoners to low level adventurers.  Also monsters of base intelligence that are large and powerful.<br/><br/>Common: 500 gp - Important members of society and the ruling class as well as mid level adventures and many of the intelligent foes they would face.  Even kings often fall here.<br/><br/>Greater - 2000 gp,  Rulers of powerful empires,  high level adveturers and their foes.<br/><br/>Grand - 5000 gp,  Near epic through low epic.  Here is your Balors,  Titans,  Great Wyrm dragons.<br/><br/>Planar - 20,000, This is for "standard" monsters beyond the first couple epic levels.  It's mostly a reserved tier so that every epic encounter isn't full of cosmic level Souls.  Our PC's are probably this on the verge becoming Cosmic.<br/><br/><br/>Cosmic - Priceless,  Adventurers around level 25 and above as well as unique cosmic entities.  The Malcanthet avatar printed in fiendish codex one would be grand or Planar.  Malcanthet herself is this.<br/><br/>-----<br/><br/>This is just a rough idea of what I feel would work well. Hit dice or CR don't feel right.  Dinosaurs have a massive amount of hit dice but they're really just animals. Their souls can't be worth much at all. Where the king of an Empire might just be a mid-level aristocrat but his importance makes him much greater than his CR would indicate.  That and a level 20 wizard should not be the same as 20 level one warriors.  A level 20 character should be worth hundreds of common man souls.