In keeping with your question, I'll leave out instances of human body part use for purely utilitarian reasons (organ donation) and focus on things done for symbolic reasons (dehumanizing, revenge, magic, etc), especially with reference to victims of political persecution or on the losing end. Do correct me if I've interpreted your questions wrongly :)
Recent Conflicts and Witchcraft
Examples of cannibalism appear sometimes in certain African and Middle-Eastern conflicts, such as Syria, the Liberian Civil War, etc. Aside from humiliating opponents (it is reported that "hearts and other organs (were) being cut out of victims and forced on their families to eat" in Congo), or for revenge, oftentimes it was also believed that human sacrifices would give one magical powers. Liberian Ex-Warlord General "Butt-naked" believed that sacrificing a young child and consuming his/her heart would satisfy the devil. The BBC reports that Tanzania had trouble with its underground human skinning trade in 2006 where the skins would be exported to West Africa for use in magical rituals.
Nazis (Regarding the historicity of the allegations)
It seems that the allegations about Nazis turning their victims body parts into products is fairly well-backed by evidence. There is still a large stockpile of hair at Auschwitz which was collected by the Nazis for use in blankets, and other textiles. Recently, the Deputy Director of the Auschwitz memorial site, Dr Jacek Lachendro, claims that 1.95 tons of human hair was found in a Schaeffler plant after the war.
The Auschwitz memorial museum confirms that small-scale production of human-fat soap occurred, and was used to wash autopsy rooms. A jar of human-fat soap is stored at the Hague. The Wiki on this is pretty comprehensive.
According to Toshiyuki Tanaka, ritual cannibalism was done to 'to consolidate the group feeling of the troop'. His documentation on Japanese war atrocities can be found here. Unfortunately, further documentation on this topic is scant.
Trophies and Souvenirs
American Soldiers and Head-hunting
Taking home Japanese skulls as a keepsake is fairly well documented in sources such as Trophies of War: U.S. Troops and the Mutilation of Japanese War Dead, 1941-1945.
This excerpt is taken from Skull trophies of the Pacific War: transgressive objects of remembrance.
Sledzik and Ousley (1991: 521) report that skulls were missing from
about 60 per cent of the remains of Japanese war dead repatriated from
the Mariana Islands in 1984. A Japanese priest who visited Iwo Jima
regularly since 1952 to conduct ceremonies for the dead reported
similarly in 1985 that skulls had been taken from many of the remains,
presumably for souvenirs (Ross 1986: 357-9; see also Fussell 1988:
51). Such evidence suggests that a substantial quantity of human
remains may have been imported into the United States during the war,
and perhaps also in the immediate post-war years, though US customs
took measures to prevent it.
Similar incidents were reported during the Vietnam War
An unfortunate side-effect of tourism was an increased demand in shrunken heads. In New Zealand, Mokomokai, or preserved heads of Maori warriors that were decorated with tā moko tattooing were prized souvenirs.
According to CIRCULATION, ACCUMULATION, AND THE POWER OF SHUAR SHRUNKEN HEADS, demand for shrunken heads led to an increase in warfare amongst the Shuar in order to maintain production of shrunken heads (tsantsas):
The concurrent increase in intergroup warfare suggests that some Shuar
may have begun producing tsantsas for export (Bennett Ross 1984:89–90;
see also Steel 1999:754–759). Tsantsas, then, did begin to confer on
the Shuar considerable material “blessings.”
Siege of Cawnpore
Sepoy prisoners were forced by the British to lick bloodstains off the walls and floor as a form of punishment.
In Surviving Tribal Cultures
Cannibalism continues in various primitive cultures. It is the punishment for witches in some Papua New Guinean tribes, such as the Kombai. A dying victim whispers the name of the witch who killed him on his deathbed after which his relatives execute the witch. Oftentimes this is merely used as a pretext for the abuse of marginalized members of the community, such as women.