I have to say that Ralph Fiennes' portrayal as Amon Göth is probably #1 on my list. Also I think Thomas Kretschmann is always perfect at acting a German officer, he most likely has done the most German WW2 roles ever . Bruno Ganz's role of Hitler was superb too, simply amazing.
Fiennes in Schindlers List is certainly among my favorites, as well.
His strongest scene - and the one in which he gives us the deepest insight into the character's psychology - has to be the scene with Helene Hirsch in her quarters in the basement.
It is clear that he is attracted to her, while she is nothing but terrified of him. At first he tries to be polite and charming and even goes so far as to offer her good references for a post-war job - A completely absurd and almost comical offer: If Nazi Germany wins the war, she literally has no future; if they lose, references from a concentration camp commandant are hardly desirable.
His efforts (naturally) lost on her, he gets increasingly unsure and anti-Semitic Nazi ideology starts to creep into his monologue; realizing this, he only gets more nervous and unsure until it all shifts into an outburst of blind rage and aggression.
We come to understand that he is perfectly capable to function in the commandant/prisoner relationship or in his perceived master race/subhuman world view, but not in normal human-to-human interaction.
As much as we despise his actions, we almost feel sorry for this depraved, lost soul. (A bit like Fiennes' torturing and tortured serial killer in Red Dragon, actually.) Awesome acting!
Other outstanding performances that come to my mind were - in no particular order - Kenneth Branagh as Reinhard Heydrich in Conspiracy or as that Gestapo officer in Swing Kids, Justus von Dohnányi as Gauleiter Stein in Napola, Donald Pleasance as Heinrich Himmler in The Eagle Has Landed and Harvey Keitel in The Grey Zone.
(And, of course, Christoph Waltz' incredibly brilliant work as Hans Landa in Inglourious Basterds; although this larger-than-life character probably doesn't count as a realistic Nazi figure.)
Bookmarks