>Never heard of Jasenovac. I have heard that there were gypsies, Hungarians, Poles, Russians, French, and many others killed though. The Jews were the largest group - I believe - targeted by the Germans, so it makes sense to me that they would be the best known. Oh, and there were Germans killed too. By Germans.
On the same note, the German communists were quite strong, and at some point they were surely stronger than the Nazi party. Unfortunately, the rigid hierarchy of the movement at the times (read: Stalin's dictatorship over the movement) found that there were more important enemies to fight at the time. The Nazi party had the "socialist" word in its name after all, and eventually the Molotov-Ribbentrop pact sealed the policy: communists didn't dare try anything against Nazis between 1939 and 1941, and by that time they weren't to be seen anywhere. It's not a coincidence that a communist was framed for the burning of Reichstag - at that time, they were still a threat to the new regime.
OTOH, there's a monument to a German soldier somewhere in central Serbia. The guy flatly refused to shoot the lined-up peasants, and was shot together with them.