"Armagideon Time" (The Clash)

"Armagideon Time" was the b-side to the single "London Calling," a song which always gets heaped with praise.  Granted, it's not unfounded praise.  After all, it's the title track to one of the most kick-ass double albums of all time.  
But I think the cover of reggae artist Willi Williams's "Armagideon Time" actually delivers palpable feelings of late Cold War-era paranoia and fear better than "London Calling" does.
Maybe it's because "London Calling" paints a picture of a post-Armageddon world; the bomb has already dropped, and the deed is done.  On the other hand, "Armagideon Time" anticipates the turmoil that's coming.  It's that sense of impending doom that makes the song send shivers up your spine.
It's also just a great groove with a rocksteady beat and sick dub effects.  It also has the distinction of band manager Kosmo Vinyl breaking in at the 3:00 mark over the recording studio intercom and telling the band, "Ok, boys, let's have you out!"  (Joe Strummer had told Vinyl to stop them at 3:00 because he believed most radio-friendly singles were 3:00.)  But then Strummer responds to Vinyl "Ok, ok, don't push us when we're hot."