KFOG has an insta-poll up at the Morning Show page, but their choices are limited. I voted for Reservoir Dogs, but that is actually polling 4th out of 5 right now.
The one that immediately leapt to mind & which I emailed them (there's a link for that, too) was "Sympathy for the Devil" in Coming Home.
You know, the scene where Jane Fonda is working at the VA hospital with her new best friend Vi, & Vi's younger brother Bill* (clearly suffering from acute PTSD) locks himself up in the room & kills himself by injecting air into his bloodstream. That was (imho) a pretty effective use of a song in a movie.
*Bill was played by Robert Carradine of the Carradine acting dynasty, later famous to my generation for being the chief nerd in all the Revenge of the Nerds movies, and known to today's teens as Lizzie McGuire's father.