This is hard. My favourite song changes quite regularly, but thinking about this my mind keeps coming back to one song:
David Bowie - Heroes
http://www.youtube.com/watch?v=zQFuNHCMF2Y&feature=av2n I'm not sure what it is about this. The lyrics, the Bowie/Eno wall-of-sound or Robert Fripp's wailing feedback, but this is pretty much the perfect Bowie moment. Over-exposure and terrible terrible covers (I'm looking at you Oasis) can't tarnish it.
While the record is sublime, especially the album version, it has a whole different life as a life track - a highlight of many a bland 'stadium event' (for example Live Aid and The Freddie Mercury Tribute (the last time Bowie performed with Mick Ronson)). I was fortunate enough to see Bowie on the 'Reality' Tour - which seems to have been his swansong - and Heroes was one of the defining moments of the show, Earl Slick proving why Bowie came back to him time and again.
I can listen to this track again and again and never get bored...
Bubbling under:
Being Boring: Pet Shop Boys
Round & Round: New Order