A song that makes you fall asleep. I've chosen a song that helps me fall to sleep rather than one that is so blargh you fall asleep to avoid it.
The Four Seasons by Antonio Vivaldi wins this round. Years ago, when I had trouble sleeping as a kid (it's been an issue for a long time) my mum would play a cassette (yep, technology ruled) of the Four Seasons to help distract my brain as I drifted off to sleep.
The result is each season means something slightly different to me. Depending on which side of the tape we were up to (that fangled technology required these accommodations) meant I either started with Spring or Autumn. So, those were the signals for my brain to start getting to sleep. If I heard Summer or Winter start I knew I was having one of 'those' nights aka taking forever to get to sleep.
Spring and Autumn are such triggers now, that I tend to almost not-hear them. I've gone with an excerpt of Winter as the show'n'tell. Plus I think the link is kinda awesome (I'm a sucker for fancy masques). Enjoy!