At the moment, Earthling by David Bowie (I know, an album not a song!). My song of the moment changes daily, depending on what mood I'm in. I'm in the process of building up my music collection - my music buying pretty much ground to a halt in the early-80s - co-inciding with the birth of my son. Now I have the time, and a bit of spare money, I can pick up where I left off. Pretty much anything by Joni Mitchell, Jethro Tull or Leonard Cohen will be near the top of my current listening.