One of the most haunting and beautiful songs of all time is singer/songwriter Leonard Cohen's "Hallelujah." Known as a secular hymn and described by singer k.d. lang as "the struggle between having human desire and searching for spiritual wisdom. It's being caught between those two places," the song found popularity with the sorrowful performance by Jeff Buckley on the film Shrek.
A Capella group Pentatonix performed their own rendition of the song for their Christmas album A Pentatonix Christmas. The song was a big hit and has millions of views!
From their bio:
Three-time Grammy® Award-winning and multi-platinum-selling artist Pentatonix (presently comprised of Scott Hoying, Mitch Grassi, Kirstin Maldonado, Kevin Olusola, and Matt Sallee) formed in 2011 during NBC’s The Sing Off. Shortly after winning NBC's a cappella singing competition the band separated from their record label and subsequently turned to YouTube to promote their debut independent releases. The Pentatonix YouTube channel currently boasts 18 million subscribers and has yielded more than 4.5 billion video views, including “Hallelujah" (500 million views), "Daft Punk" (325 million views), and "Mary, Did You Know?" (230 million views).