One still unresolved aspect of World War II is the still missing art which was looted by the Nazi's from museums and Jewish collectors. Hitler had a distinct taste in classic artwork, and envisioned a massive museum in Germany with the finest collection in all of the world. On result of his taste was that all contemporary artists were seen as "degenerate art" and was toured around Germany as examples of art which would harm your mind.
One of the great tragedies to the world is Hitler's cultural change policy for much of the countries he invaded. The main cultural aspects of these places ( art, furniture, architecture) were purposely destroyed, and instead German propaganda art was heavily promoted. Records show that in order to boost the market for this art, Hitler himself bought hundreds of Nazi art pieces every year. The world lost a massive amount of great art, but further many people lost their cultural identity, history and intellectual independence. Family's in concentration camps had their photo albums burned, assets seized, and heirlooms plundered.
In order to fill Hitler's Fuhrermuseum, Nazi's plundered art collections by prominent Jewish collectors and gallery owners. The Nazi's took meticulous records regarding the art. Each piece was lettered and numbered by collector and location as to where/who they were taken from. This has been enormously helpful in recent years to help return them to the heirs to the rightful owners.
The Meadows Museum on SMU's campus is home to many great works of art, however in 2010 it was discovered that three of their most famous paintings were actually looted by the Nazi's from a prominent Jewish collector. The first painting found to be a looted piece was Saint Justa by Bartolome Esteban Murillo. Robert Edsel was doing research for his book when he came across the piece and recognized it. The proof of the looting was marked on the back of the painting. The code, "R1711" was written on the back of the paintings indicating that it was stolen from the Rothschild family's collection. When they looked through the rest of the paintings in the museum, two other paintings had Nazi codes.
The work was returned to the rightful owners, the decedents of the Rothschild family, now living in America. In an era of mile high prices for art, and status snobbery, returning the art to the rightful owners is one of the honorable aspects of the art world. The Rothschild's were Jews which fled their Vienna home to escape Nazi rule had an amazing art collection. The conditions of their escape were that they would have to turn over their art collection and much of their assets to the government. This was actually documented by their next door neighbor, William Shirer, an American correspondent for the war. He wrote, "I myself, from our apartment in Plosslgasse, watched squads of SS men carting off silver, tapestries, paintings and other loot from the palace." 
Part of the issue with returning the art is that tracking down the heirs is difficult. And further, figuring out which pieces were stolen is getting more and more difficult as time goes on. The markings which the Nazi's put on are often worn off. As such, many collectors and museums have no idea they have this plundered art work.
I wonder how the value of the art which Hitler plundered will change after it is returned to the owner. In one respect, I could imagine it would raise the price because it has a large historical significance, however in another I could see it having a lower price because it is seen as having been in the hands of the Nazi's.
There are a lot of questions about antiques, and art regarding being returned to where they came from. In the case of Nazi's it is clear that the plunders of Europe should be returned to the rightful owners. However, the treatment of other artifacts is still a moral grey zone. Things which are stolen should be returned. Yet, there is no simple answer for all antiques and art. Should some Picasso's be returned to Spain because of the artist's Spanish decent? In 2003, the British Library refused to return The Lindisfarne Gospels which were stolen from the Durham Cathedral in the 16th century, will not be returned due to the fact the document is incredibly fragile, and the current location allows the world access. 