well, Neil Young's "It's a Dream" does it to me almost every time. On the CD, when his voice breaks as he goes for the high part of the melody ("it's only a dream...") and then his sigh of inevitably ("and it's fading now, fading away....") - I pretty much lose it right there. Sometimes I think that's the most beautiful song I've ever heard. Dave Matthews' "Stay or Leave" will always remind of a particularly low period for me and can take me by surprise sometimes. Lucinda Williams' "Sweet Old World" can hit pretty hard sometimes too. wow, at first I didn't think I had an answer for this topic!