I think asking how music can move you to tears without context is like asking why people laugh. 
Julian Lennon’s song,Valotte when it first came out. Lots of emotions hearing John’s son singing.
Johnny Cash’s cover of Hurt. Maybe I read too much into it but it sounded very much like he was singing about himself.
Beethoven’s Ninth has done that to me several times, always during the choral movement. Mussorgsky’s Pictures at an Exhibition has done it to me as well.
One night I had my radio tuned to the local classical station while I was reading. When they started playing Pachelbel’s Canon, I was barely even aware of the radio, but by the time the Canon had finished I was sitting at my desk with my mouth hanging open and tears running down my face.
Several times the recording of Duke Ellington’s orchestra playing “Diminuendo and Crescendo in Blue” at the Newport Jazz Festival left me wiping tears from my eyes. The sheer joyful exuberance of that piece is overwhelming when I’m in the right mood. Johnny Hodges’ sax solo will curl your toes.
Warren Zevon: Renegade, The Heartache, and Keep Me in Your Heart for a While.
Johnny Cash’s When the Man Comes Around.
Willie Nelson singing J.J. Cale’s Gravedigger.
Harry Chapin’s Better Place to Be.
Hank Williams, So Lonesome I Could Cry and Lost Highway.
The Beatles, You Got to Hide Your Love Away & the Turtles Love Can Turn Like the Seasons, played continuously after my first girl friend dumped me and I became a 15-year-old drama queen.
O, Canada and La Marseillaise. Performed by a church choir accompanied only by a pipe organ.
Damn, I didn’t realize I was such a softie.
Haven’t heard this one in a while but ‘Acoustic Medley’(Summer 1971) by Bob Marley is incredible. I welled up and broke down(me, not the car lol) listening while driving from Maine to New York on my way to see my girlfriend in some heavy heavy snowfall. Wicked cool! Strangely she was the one who bought me Handel’s Messiah on CD the winter prior. Strange that it’s been mentioned here over and over!
When I look at the music mentioned in this thread, and I think about the songs that have made me tear up in the past, I feel like a complete hick:
He Didn’t Have to Be, Waiting on a Woman, Whisky Lullaby, Brad Paisley
Travelling Soldier, Dixie Chicks
She Thinks She Needs Me, Andy Griggs
Austin, Blake Shelton
Normally, it’s the combination of these songs and an already fragile emotional state that sets me off; I could listen to any one of them now and be fine.
Interesting that you should say this. There have been several points in my life when I have found myself completely overwhelmed by a piece of music, and rather than cry, my reaction was to laugh. I have no explanation.
I can, however, think of two occasions when singing a song (actively participating, not just listening) sent me into complete waterworks.
First was the funeral of my high school principal. As the casket was carried from the church, someone in the congregation began singing the school fight song. Slowly. Everyone else joined in, and there was not a dry to be seen anywhere by the time it ended.
The second was my college graduation. The ceremony concluded with two verses of America the Beautiful, and for some reason, as I sang them, the lyrics completely crystalised and I understood them in the deepest recesses of my soul. And suddenly I was bawling.
Bjork- anything, really.
That damned chorus on the battlefield in Branagh’s “Henry V.”
That damned pop song about “15, there’s still time for you.”
The version performed by Aaron Neville over the credits of the film “Alive” is pretty amazing. I think this is a live version of it- http://www.youtube.com/watch?v=aR-TxbVdgok&feature=fvst