F.E.A.R. When Alma liquefies everybody, leaving only the skeleton.
Mass Effect 2 when Shepard finds out the true fate of the Protheans (the background music added some spice to the revelation).
Skyrim when I was visiting Falkreath two dragons appeared at the same time, BUT the first dragon died when it touched the floor leaving me to slay only the second dragon.
Still on Skyrim when I left the Wolfskull Cave after I finished the quest "The man who cried wolf", a dead dragon appeared before me and I got a free dragon soul.