The most haunting music you ever heard?

Dawn Upshaw, Sergio & Odair Assad Orpheus Chamber Orchestra, "Il la Luna Esta Muerta" on White Moon - Songs to Morpheus

John Williams and Yo Yo Ma, "The Invasion" on Seven Years in Tibet (Original Motion Picture Soundtrack)

Branford Marsalis Quartet "Eternal" on Eternal

Rickie Lee Jones "Comin' Back to Me" on Pop Pop

Jack Johnson "Belle" on In Between Dreams

Check out the album "The Swell Season" by Glen Hansard and Markéta Irglová. The album includes studio versions of many of the songs from the soundtrack of the movie "Once". The mostly (entirely?) acoustic album is some of the most beautiful and haunting song writing, singing and playing I have heard all in one place in a long time. For audiophiles, I think "The Swell Season" has higher production values than the soundtrack, although the play lists are slightly different. You might want to watch the movie before buying either CD.