Ear

Ears are, beyond being hearing organs, specific trophies for some of the more violent people of the wasteland.

Fallout 2
If you have about 160% in Unarmed, you can bite the Masticator's ear right off in the Reno boxing ring. But, if you have less than 110 hit points, the Masticator can bite yours off. The Masticator's ear is worth $750, but yours will cost you 1 point of Charisma.

Fallout 3
Ears can be found on good characters (like Abraham Washington or Agatha Egglebrecht) when you have the Contract Killer perk.

Daniel Littlehorn from Littlehorn & Associates, located at the Scrapyard, rewards you with 15 caps and bad karma for each ear. This is the bad Karma alternative to the Lawbringer perk, in which you collect fingers instead of ears.

While you cannot kill essential characters, an ear will spawn in their inventory each time they are knocked unconscious. These can then be pick-pocketed from them.

Fallout: New Vegas
Every Caesar's legion soldier you kill has a chance of having this on his corpse after starting the associated unmarked quest An Ear to the Ground.
 * See Legion ear for more information.