I grew up listening to the Beatles (from a very early age), but the first song that I remember hearing and understanding was
<spoiler=A Day In The Life> This isn't the version I first heard, but it's my favorite. It's a better, more modern mix than the original, without the fade in/out from Sgt. Pepper's Lonely Hearts Club Band (Reprise)
I am now a veritable fanboy/aficionado, and have almost everything they ever released, including live shows and the Anthology series of CDs and DVDs. (338 Songs and 10 DVDs...yeah...)
__
I first heard "play Crack The Sky" performed live at a student show, after which I immediately found the orignal.
<spoiler=Play Crack The Sky> I F***ING LOVE THIS SONG.
I loved what I heard, decided to get more, and more, quickly becoming one of my favorite bands. I have all four albums, b-sides and live shows.
__
"White Shadows" and "Clocks" got me hooked on Coldplay.