The author of the excellent (and previously mentioned) 60s/70s soul music blog Funky 16 Corners has put together an awesome compilation album available for free download, called Rubber Souled, featuring soul covers of Beatles classics; the results are intriguing, from Stevie Wonder's funked out version of We Can Work It Out to a nightmare inducing Bill Cosby cover of Sgt Peppers.
Long before Robert Johnson ever went down to the crossroads, violinist & composer Niccolo Paganini was rumored to have sold his soul to the devil in exchange for musical ability. Evidence against this theory: Paganini's 5th Caprice actually prevented the devil from stealing The Karate Kid's soul (the devil settled for stealing Ralph Macchio's career instead). Evidence in favor of this theory: When played on acoustic guitar, the virtuosity in his 24th Caprice really seems supernaturally inspired. For my money, however, the perfect storm of ominous music & stringed instruments comes together in this version of Carmina Burana (mp3 direct download), arranged for solo banjo.