Ooh, now there's a leading question.
It's impossible to single out one track. There are several that I have to mention.
Oxygene parts 2, 3 & 4 by Jean Michel-Jarre
Not only were these magnificent instrumentals some of my earliest musical memories, but this is really what sparked my interest in electronic music - even at such an early age! Oxygene is probably my all-time favourite album.
Love Action/Hard Times by the Human League
Again, synth music, that I loved when I first heard in 1981, at the age of about three. "Love Action" remins my favourite pop song of its kind.
Wild is the Wind/Golden Years by David Bowie
Again, this was released in 1981 and forms part of my earliest musical memories. Bowie's voices fascinated me, as did the photo of him on the album sleeve - a wonderful mono shot (best photo he ever had taken!) with just his eyes in colour. And two of his greatest tracks and certainly my favourites.
But finally, a track that perhaps had more significance than any other...
Steam by Peter Gabriel
Perhaps not Gabriel's greatest track, although arguably his finest "pop" moment since "Sledgehammer". It wasn't so much the song though, but the video. The groundbreaking videos for "Steam" and "Digging in the Dirt" totally blew me away at the time, and also came at an important time in my teens, where I was trying to decide what sort of career I wanted – the visual impact of Gabriel's work made that decision for me.
Those videos also introduced me to Gabriel's music, as I didn't know of him before then, and I have been enormously passionate about it ever since. Discovering Peter's amazing back catalogue (and fantastic album covers and song videos) really inspired me on so many levels, and also turned me into a music "fan".
From here, I was inspired to rediscover David Bowie, who I had not really listed to since playing the aforementioned single as a child, and that gradually led me to discovering other acts such as Simple Minds, Sting, Depeche Mode, Gary Numan and John Foxx.