"Beauty is in the eye of the beholder." In our world, it means that only certain people know how to appreciate the beauty of something. In the world of D&D, with Wizards summoning comets every other day, and "Take care of the zombie infestation" has transformed from a seemingly impossible task to yet another household chore, it would probably mean that a beholder's eye on a wall is beautiful to look at. This is very true. We hang moose heads on our walls, but what about in D&D, where moose do not exist? Then they hang the equivalent of moose, such as Beholder Eyes or Dragon Heads.
When your party slays a Black Dragon, do they ever cut off it's head to show off to others? Or maybe keep its blood, which can revive dead people? I know I would. If PCs do such things, and then one of the PCs resigns, the DM knows he has hit the jackpot. If he is a creative and resourceful one, the players can almost confirm that he will make the resigned guy an owner of a tavern.... with the Black Dragon head on the wall.
Also, you can be sure that the players will need his help to kill the rampaging horde of orcs. After all, Moonstone the Wizard was useful in the past(cue epic flashbacks of times when Moonstone saves the party using his _______ spell/ritual), so why not ask for his help now? His pay is, by the way, much easier to get since:
1) He probably feels a sense of loyalty and is eager to get out his old Staff of Annihilation+1 again
2)He knows the value of a Goblinmade Magic Axe+1, unlike other tavern owners which require you to search for days for a cloth to mop the bar table.....
This is what Dungeon Mastering is all about. The expressions of shock on the players' faces when they see old Moonstone again, and the expressions of relief on the players' faces when they realize that means NO STUPID HUNTING IN THE MOUNTAINS FOR A ****ING CLOTH!
This could be continued in a cycle, with one of the PCs bringing back the Orc King's Head(or scepter or whatever).
In conclusion, Trophies can be a powerful element in your roleplaying if you know how to use it properly. They could change the course of the story.... and not to mention that instant increase in renown points once you start showing off that Death's Scythe +8 you got from the Grim Reaper...