Gitr noted on his blog yesterday that after he killed Frostmaw recently, he noticed something strange. Much like the foot of the Marine in the aforementioned movie, it's hand was still moving -- clenching and unclenching his staff -- even though it was clearly dead. I don't know if this is something that can be duplicated every time, but it would sure freak me out.
About once or twice a month I get a somewhat more amusing graphical bug where the mob keeps "looking at me" even after it's dead, causing the body to spin on the ground if I run around it in circles.
While some bugs are annoying, some like these are amusing and even interesting. What silly in-game anomalies like this have you seen?