Shape-Shifter wrote:

So, 68. There can be only one choice for me. KingDaniel, you may remember this one from a Simpsons episode, the church lady organist nearly died playing it. 
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I haven't even listened to it yet and I know what it is
In 1968 Johnny Cash performed a concert at Folsom Prison and sang Folsom City Blues, which would become one of his many signature songs. Supernatural has an episode of this name though I don't know if they included the song in it.. perhaps someone can enlighten us.