Fuzzy,
Maybe it's just me, but certain songs by Pink Floyd, Nickleback, Rolling Stones, Rare Earth, (there's an old one), Dave Matthews do it, usually when I am riding my bicycle, motorcycle, walking or running, or sometimes driving with no distractions. Also, I can get the same chills (endorphin rush) just imagining these songs the in my head, and finally, yeah I know I am a bit weird, from thinking about a problem with science/math and coming up with a possible solution (I know that is not music), just wanted you to know that music is not the only form of mental stimulation that causes it. Sometimes when I read something that is surprising or I have never heard of before causes it too. You have seen this happen in the synesthesia thread.
To sum up:
listening to certain music
imaging listening to certain music
realizing a possible solution to a problem
reading about surprising information
Rhody...