"Nazis get results!" Oh, it is SO easy to quote that out of context.
I'm bored with the zombies because they make no sense as an enemy. One of the most-read articles on Cracked.com, "7 Scientific Reasons a Real Zombie Apocalypse Will Fail", said the zombie is a creature designed for failure. Its natural enemy, living humans, are also its prime food source and only means of reproduction. Zombie fiction never explains how zombies aren't stopped by the CDC or the military before it goes into full plague mode. I find really annoying when they switch gears and go "No, wait! It's the Humans Are the Real Monsters!", and I find that insulting.
Nazis, however, are guilt free to kill because most of their leaders and original founders were practicing occultists who sound like they jumped out of an old comic book, because their beliefs and methods were so evil. It's even fun to blame them for everything wrong with the world now. I like it when their is a reason to make the bad guys Nazis or Nazi-like, such as HYDRA from Captain America: The First Avenger, which had all the superscience and magic that the real world Nazis WISH they had in the war.
I can see why those two groups are used as bad guys in movies and video games so much, because it's so easy to make a political statement when you identify an enemy by their country of origin or religion, which is why we don't see a whole lot of Middle eastern terrorists in popular fiction, even though we're still at war with them.