Nebel, by Rammstein

Why it's the saddest song:
"The last kiss was so long ago, the last kiss, he does not remember it anymore..." The song is about the death of a loved one, and what is ironic about this is the title; when you flip it backwards, it says leben, which means life.

Strike against it:
Till Lindemann's gruff voice doesn't exactly match the mood of the song, but even then, it still sounds pretty great.