Here is a list from Pitchfork; the Beach Boys’ "God Only Knows" takes first place. The selections are excellent (head to iTunes), but I would have opted for the Beatles’ "Rain" and the Byrds’ "Eight Miles High." You’ll find links to their top 200 picks as well.
Daniel Levitin’s This is Your Brain on Music: The Science of a Human Obsession — is a new book on how music affects our brains. Here is an introduction to the book.
Addendum: Here is an interview with Levitin.