Elvis Costello is in my mind one of the brilliant song writers we have. What I like especially about Oliver's Army is the contrast between the pop style tone and the dark lyrics. I reckon a lot of people know the song and probably made up lyrics to sing along it, because they cannot actually believe how grim the real lyrics are.
But in general, Costello's muisc, has had a stark influence on me, when I try to put some music together.