Timothy Snyder's Bloodlands: Europe Between Hitler and Stalin made a lot of noise when it came out in 2010, mostly because of its perceived moral equation of Hitler's and Stalin's crimes. Personally, I am not sure Snyder is even interested in the moral question though, for me he simply states that there is a striking geographic overlap in the areas where both Soviet Communists and German Nazis had most of their victims.
These Bloodlands - between Eastern Poland, Belarus, Ukraine, the Baltics and Western Russia - suffered from the Ukrainian famine, the concomitant invasion and occupation by Germany and the USSR in 1939, followed by a second invasion for the formerly USSR-occupied regions in 1941, the starvation of millions of Soviet soldiers, the Holocaust in both its early (bullets) as well as late (gas) stages, and finally reconquest by the Red Army with the Wehrmacht leaving a bloody trail on its way back to Germany.
It's essentially an absolutely horrifying account of the unprovoked killings of 14 million civilians in a 12-year span.
There is little that I feel I can truly contribute to this debate, which involves far too many outlets and national perceptions as it is (hier in der Zeit, the NYRB, ou Le Monde) and I will let historians figure out whether Snyder's Fascism-Communism comparison holds true or not:
Hitler and Stalin thus shared a certain politics of tyranny: they brought about catastrophes, blamed the enemy of their choice, and then used the death of millions to make the case that their policies were necessary or desirable. Each of them had a transformative Utopia, a group to be blamed when its realisation proved impossible, and then a policy of mass murder that could be proclaimed as a kind of ersatz victory. (Wikipedia)
Let me just say that as someone possessing slightly above average knowledge of the history of the Third Reich I discovered relatively little new in Bloodlands concerning the atrocities committed by the Germans - and, yet, even there specific events especially in Belarus and Warsaw I was little familiar with - while the account of the Soviet crimes perpetrated during those years were revelatory and for the most part completely new to me.