Perhaps the most awesomely named of all the rare / unique weapons in Fallout New Vegas is Recompense of the Fallen, the rare version of the dogtag fist. Watch this video to learn how to find it in Cottonwood Cove.
From the Creator:
There is one in Cottonwood Cove. The centurion is wearing it you can get it if you kill him. Sometimes it will not be on him. If it is not check the desk in his bunker up the stairs and to the right at the Cottonwood Cove HQ building.