I can't say that I only have one.

Cat Stevens - "Father and Son". Whenever I hear this song, I think of my old man and just fall in a crying heap. I leave parties when this song plays.

Bob Dylan - "The Lonesome Death of Hattie Carroll". Fifty years later; nothing's changed. I bury a rag deep into my face every time on cue.

Red House Painters - "Medicine Bottle". This song just ain't right. I don't understand how writers of this kind of music can continue living; I've seen ropes and doorhandles just listening to this song.

edit: and, of course, "Hurt" by Nine Inch Nails. I've heard Johnny Cash's version; I guess I just haven't lived enough yet to understand it. Cash's version portrays a life lived (a life lived though, mind you) with enough regret to weigh heavily enough on your shoulders that it pains you; NIN's version, however, portrays a life, well, observed, inside, not inside a home - there was no home for the author of that song when he sang it - but inside yourself and inside your mind, dripping with self-loathing that he's physically and mentally unable to cope with. I don't know how other people have interpreted Cash's version, but I've never played it on repeat naked save for modesty in an empty room blue-nailed and ashamed.